Lit Interior.pdf

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William J. Fielder PE, m. IESNA
With contributions by
Frederick H. Jones PhD
The Lit Interior
OXFORD AUCKLAND BOSTON JOHANNESBURG MELBOURNE NEW DELHI

Architectural Press
An imprint of Butterworth-Heinemann
Linacre House, Jordan Hill, Oxford OX2 8DP
225 Wildwood Avenue, Woburn, MA 01801-2041
A division of Reed Educational and Professional Publishing Ltd
A member of the Reed Elsevier plc group
First published 2001
© William J. Fielder and Frederick H. Jones 2001
All rights reserved. No part of this publication may be reproduced in
any material form (including photocopying or storing in any medium by
electronic means and whether or not transiently or incidentally to some
other use of this publication) without the written permission of the
copyright holder except in accordance with the provisions of the Copyright,
Designs and Patents Act 1988 or under the terms of a licence issued by the
Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London,
England W1P 0LP. Applications for the copyright holder’s written
permission to reproduce any part of this publication should be addressed
to the publishers
British Library Cataloguing in Publication Data
Fielder, William J.
The lit interior
1. Interior lighting 2. Lighting, architectural and decorative
I. Title II. Jones, Frederick H. (Frederick Hicks), 1944–
747.9'2
Library of Congress Cataloguing in Publication Data
Fielder, William J.
The lit interior/William J. Fielder; with contributions by Frederick H. Jones.
p. cm.
Includes index.
ISBN 0-7506-4890-2
1. Interior lighting. 2. Electric lighting. 3. Lighting, architectural and
decorative. I. Jones, Frederick H. (Frederick Hicks), 1944–
TH7703.F54 2001
621.32'2–dc21 2001053540
ISBN 0 7506 4890 2
Composition by Scribe Design, Gillingham, Kent, UK
Printed and bound in Great Britain by MPG Books Ltd, Bodmin, Cornwall

Preface ix
Chapter 1. The design medium 1
The process of vision 1
Light mechanics 4
Transmission 5
Refraction 6
Reflection 6
Absorption 7
Physical factors 8
Size 8
Contrast 8
Luminance 8
Time 8
Light quantity 9
Light quality 11
Glare 11
Brightness ratio 12
Diffusion 12
Color rendition 12
The psychology of lighting 13
Summary 16
Exercises 17
Chapter 2. The design tools 19
Lamps – the light source 19
Lamp theory 19
Incandescence 20
Photoluminance 20
Color temperature 22
Color rendering index 23
Contents

Lamp – major types 24
Incandescent lamps 24
Standard incandescent lamps 24
Tungsten halogen lamps 26
Infrared reflecting lamps 27
Incandescent lamp benefits 27
Incandescent lamp drawbacks 27
Incandescent lamp uses 28
Fluorescent lamps 28
Rapid start fluorescent lamps 29
Instant start fluorescent lamps 29
High output and very high output fluorescent lamps 30
Compact fluorescent lamps 30
Other fluorescent lamps 30
Fluorescent lamp advantages 31
Fluorescent lamp drawbacks 31
Fluorescent lamp uses 31
High intensity discharge (HID) lamps 32
Mercury vapor lamps 34
Metal halide lamps 35
High pressure sodium lamps 37
Low pressure sodium lamps 39
Ballasts 40
Fluorescent ballasts 40
Magnetic fluorescent ballasts 40
Hybrid fluorescent ballasts 40
Electronic fluorescent ballasts 40
High intensity discharge (HID) ballasts 41
Reactor ballast 41
High reactance autotransformer ballast 42
Constant wattage 42
Constant wattage autotransformer ballast 42
Luminaires 43
Reflectors 43
Shielding and diffusion devices 44
Baffles 45
Diffusers 45
Luminaire housings 46
Luminaire classification 46
Direct illumination 46
Semi-direct illumination 48
Semi-indirect and indirect illumination 48
Luminaire photometric data 49
Lighting calculations 49
vi Contents

Zonal cavity calculations 50
Computerized calculations 55
Controls 58
Standards, codes, and design guidelines 58
NFPA-70, The National Electric Code 59
NFPA-101, The Life Safety Code 59
ASHRAE/IES Standard 90.1 59
EPACT 92 62
IES recommended illumination levels 63
Exercises 65
Chapter 3. The design process 67
Ambient lighting 68
Luminaire selection 68
Energy code compliance 80
Task lighting 82
Luminaire selection 83
Accent lighting 87
Lighting for life safety 90
Exercises 93
Chapter 4. Powering and controlling the system 94
Power 94
System voltage 94
Wire sizing 95
Panelboards 95
Load calculations 98
Wiring and raceways 98
Lighting controls 100
Switches 100
Dimmers 102
Contactors 103
Photocells 104
Timers 104
Occupancy sensors 105
Light-sensitive controls 106
Example 106
Exercises 110
Chapter 5. The contract documents 111
The project plans 113
Project specifications 116
Section 16510 – Interior lighting 118
Part 1. General 118
Contents vii

Part 2. Products 120
Part 3. Execution 124
Exercises 125
Chapter 6. The second time around – retrofitting 127
The problem 127
The solution 128
Improving luminaire optics 128
Upgrading the ballast 129
Upgrading the lamps 129
Glossary 134
Index 145
viii Contents

This book is intended as a design guide for those individuals in
the fields of electrical engineering, architecture, and interior
design who will one day design lighting systems for others to
build.
The book is organized so that an individual with little or no
training in lighting design will become familiar with the basic
principles and psychology behind good lighting before design proce-
dures are addressed. Discussions on the process of vision and the
properties of light set the stage for exploring the various tools at
the designer’s disposal for creating and manipulating light to
provide a desired effect in an architectural space.
The reader is then led through the conceptual design process,
which entails the use of manufacturer’s offerings, codes and guide-
lines for space lighting, as well as calculation methods to predict
the performance of a design. The conceptual design is rounded out
by exploring methods for powering and controlling a lighting
system.
A realistic design problem is begun early in the journey, and is
completed, bit-by-bit, as each new concept is explored and applied
to the design. Documentation of the design is the final stage of the
process, which culminates in a finished set of plans and detailed
specifications for the project. A final segment of the book, called
‘The Second Time Around’, is devoted to retrofitting existing ineffi-
cient lighting systems with new, energy-efficient components to
improve light quality and reduce the energy consumption of older
systems.
Extensive use of the Internet is used throughout the design
process. Instructions for downloading and using manufacturer’s
data, calculation engines, and other tools are included in the text
and put to use in the exercises. In the interest of continuity, Inter-
net information for this book is almost exclusively that of Litho-
nia Lighting Co., a lighting equipment manufacturer. Other
Preface

manufacturers have similar information available, and the reader
is encouraged to search the internet for other favorite sources of
information.
William J. Fielder
South Carolina, USA
x Preface

The art and science of lighting design is just that, and more: a little
artistic flair; some scientific knowledge; and last but not least, a
healthy helping of psychology. While every well-done lighting
design is attractive, and most provide adequate illumination for the
task at hand, the superior design goes the extra mile: it takes into
account the effect of the lighted environment on the eye and mind
of the human observer. This psychology of the environment is
always at play in the relationship of people and architecture, and
it can be molded dramatically with effective lighting.
Light can be thought of as a ‘building material’ much like steel or
concrete. Although structural components are needed to enclose a
space, the space has no existence for an individual until it is seen and
registered in the conscious mind. Light defines space, reveals texture,
shows form, indicates scale, separates functions. Good lighting makes
a building look and work the way the architect intended at all hours
of day and night. It contributes to the character and effective function-
ing of the space by creating the desired attitude in the mind of the
occupant. Change the lighting and the world around us changes.
The actual way the eye–mind combination evaluates light is a
complex, dynamic process, which could fill volumes the size of this
one. There are, however, some basic principles which bear consid-
eration in the design of lighting systems. In this chapter we will
consider both the process of vision, and the effect that light has on
our perception of the lighted architecture. You should come away
with a better understanding of both the physical and psychological
aspects of a lighted environment.
The process of vision
The process of vision can be roughly compared to the operation of
a radio or television receiver: there is an antenna, the eye, tuned to
1 The design medium

a specific portion of the electromagnetic spectrum; there’s a cable,
the optic nerve, connecting the antenna to the decoding device; and
then there’s the decoding device, the brain, which processes the
received information. The eye is tuned to that portion of the electro-
magnetic spectrum with wavelengths between 380 and 780 nanome-
ters (1 nanometer = 10-9
m = 1 thousand millionth of a meter)
known as the visible portion of the spectrum. Figure 1.1 shows the
electromagnetic spectrum, with the visible portion expanded.
As you can see, the visible part of the spectrum covers the
wavelengths from ultraviolet, which is commonly associated with
skin damage from the sun, to the infrared, which is associated with
the heat felt from the sun. This points out the fact that the shorter
the wavelength, the higher the energy in electromagnetic radiation.
The ‘visible’ section of the electromagnetic spectrum (see Figure
1.1), when seen simultaneously, appears as white light, such as
bright sunlight at noon on a clear day. When white light strikes an
object, part of it is reflected, and part is absorbed. For example, a
ball which is seen as blue is, in fact, reflecting the blue wavelengths
and absorbing all the others.
Our eyes are sensitive to all the wavelengths within the visible
spectrum. However, as stated before, they act as ‘antennas’ to
receive reflected light and, like antennas, they are tuned to a specific
frequency. In the case of the eye, that frequency lies approximately
at the center of the visible spectrum, and has a wavelength of 550
nanometers. This means that the sensitivity of the average eye peaks
in the yellow–green portion of the spectrum, and falls off sharply
as the limits of the spectrum are approached. Figure 1.2 shows this
as a bell curve of eye response relative to light wavelength.
Our eyes not only have to respond to a wide range of
wavelengths, but they also must automatically adjust to a
constantly varying light intensity. To see how this is accomplished,
2 The Lit Interior
Figure 1.1. The electromagnetic spectrum (source: Philips Lighting Handbook).
WAVELENGTH IN NANOMETRES

let’s take a look at the components of the eye, as shown in Figure
1.3. The ‘front end’ of the eye acts much like a camera to regulate
the incoming light and focus it on the retina. This ‘front end’ is
made up of the cornea, the clear outer layer of the eye, and the
pupil, an opening whose size is constantly being adjusted by the iris
to compensate for varying light intensity, and the lens, which uses
the ciliary muscle to change its shape to focus the light on a special
part of the retina, called the fovea. The retina contains from 75 to
150 million rods and about 7 million cones, which make up the
actual antennae tuned to the visible spectrum. The rods and cones
convert light energy into neural signals that are transmitted to the
brain through the optic nerve.
Rods cannot detect lines, points, or colors. They can only detect
light and dark tones in an image. Rods are highly sensitive, and
they can distinguish outlines of objects in almost complete darkness.
Cones are even more sensitive – they detect the lines and points of
an image, such as the words you are now reading. Cones also detect
The design medium 3
Figure 1.2. Color response of the eye (source: Philips Lighting Handbook).
Figure 1.3. Components of the eye (source: F.H. Jones).

color, and there are three types of cones present in the eye: one that
is sensitive to the blue–violet end of the spectrum; one sensitive to
the yellow–green, or middle of the spectrum; and one sensitive to
the red end of the spectrum.
The fovea contains only cones, and provides the optimal recep-
tion in brighter light conditions. Muscles controlling the eye work
in conjunction with the ciliary muscles controlling the lens to keep
the viewed object focused on the fovea. That’s why you are moving
your eyes while reading this page.
In higher light levels, the cones are the main receptors of light,
and the response of the eye to the varying wavelengths of light is
as shown in Figure 1.2. In a very low level of light, the cones cease
to function, and the sensitivity peak of the eye shifts toward the
light with the higher energy wavelengths at the blue end of the
spectrum. This is known as the blue shift, or Purkinje effect, and
it is the reason that, under very dim ambient light, the eye will
perceive blue light as inordinately bright. This is why police cars in
the US have switched from red to blue emergency lights.
As we get older, the components of the eye begin to deteriorate.
The ciliary muscles get weaker, the lens loses elasticity, and our
ability to focus, particularly on close objects, becomes less. The lens
itself yellows with age, which affects color vision, particularly the
differentiation between blues and greens. The lens also becomes
thicker and less transparent, which results in light scattering and
‘night blindness’, or extreme sensitivity to glare. The pupil gets
smaller, which reduces the overall amount of light which reaches
the retina. The result of all this deterioration is that older people
need more illumination, larger print, and more contrast in order to
see clearly – and to function comfortably.
Now that we know something about the eye, let’s take a look at
some of the mechanics of those light rays which are constantly
bombarding our rods and cones.
Light mechanics
Light travels in a straight line until it strikes a surface. It is then
modified by either transmission, refraction, reflection, or absorp-
tion. Figure 1.4 illustrates each of these light modifiers.
Light can also be modified by polarization, diffraction, or interfer-
ence by other light rays, but these play a very small part in light-
ing design. For now, let’s concentrate on the ‘big four’, and see how
they affect light rays.
4 The Lit Interior

1. Transmission
There are three general categories of transmission: Direct trans-
mission occurs when light strikes transparent material which can
be seen through. These materials absorb almost none of the light
in its passage through the material, and do not alter the direction
of the light ray. Spread transmission occurs with translucent materi-
als in which the light passing through the material emerges in a
wider angle than the incident beam, but the general direction of the
beam remains the same. Diffuse transmission occurs with semi-
opaque materials such as opal glass, and the light passing through
the material is scattered in all directions. These materials absorb
some of the light, and the emerging rays are of less intensity than
the transmitted rays. Figure 1.5 illustrates the types of transmission.
The design medium 5
Figure 1.4. Types of light modification (source: F.H. Jones).
Figure 1.5. Types of light transmission (source: F.H. Jones).

2. Refraction
Refraction occurs when a beam of light is ‘bent’ as it passes from
air to a medium of higher density, or vice versa. This occurs because
the speed of the light is slightly lower in the medium of higher
density. Two commonly used refractive devices are prisms and
lenses. A prism is made of transparent material which has non-
parallel sides. A large prism slows down the various wavelengths
of light by different amounts and can be used to divide the light
ray into its color components; smaller prisms are used in lighting
fixtures to lower brightness or to redirect light into useful zones.
Lenses are used to cause parallel light rays to converge or diverge,
focusing or spreading the light, as desired. Figure 1.6 illustrates
some refractive devices.
3. Reflection
Reflection occurs when light strikes a shiny opaque surface, or any
shiny surface at an angle. Reflection can be classified in three
general categories: specular reflection, spread reflection and diffuse
reflection. Specular reflection occurs when light strikes a highly
polished or mirror surface. The ray of light is reflected, or bounced
off the surface at an angle equal to that at which it arrives. Very
little of the light is absorbed, and almost all of the incident light
leaves the surface at the reflected angle. Spread reflection occurs
when a ray of light strikes a polished but granular surface. The
reflected rays are spread in diverging angles, due to reflection from
the facets of the granular surface. Diffuse reflection occurs when
6 The Lit Interior
Figure 1.6. Refractive devices (source: F.H. Jones).

the ray of light strikes a reflective opaque but non-polished surface,
such as flat white paint. Figure 1.7 shows the types of reflection.
4. Absorption
Absorption occurs when the object struck by the light ray retains
the energy of the ray in the form of heat. If you remember the blue
ball example, the ball reflects only the blue wavelengths of the
incident light, and absorbs all of the others. If the ball were in the
sunlight, this energy absorption would heat the ball up. Some
surfaces, like flat black paint, absorb nearly all of the incident light
rays. These surfaces, such as those of a solar collector panel, tend
to get very hot when placed in the sunlight.
With these principles in mind, you can predict how the light itself
will behave when used with the various control devices. Now let’s
look at some of the factors of light which affect the way we see.
The design medium 7
Figure 1.7. Specular, spread, and diffuse reflection (source: F.H. Jones).

Physical factors
In addition to color, the four factors which determine the visibility
of an object are: size, contrast, luminance, and time. Of the four,
luminance, or brightness, or the strength of the light falling on the
rods and cones, is the underlying dominant factor. Let’s look at
these factors in more detail.
1. Size
Size is considered because the larger or nearer an object, the easier
it is to see. A larger object, of course, reflects more total light, and
offers a stronger stimulation of the rods and cones. Also, as we will
see in a moment, light adheres to the inverse square law. This means
that the strength of the reflected light decreases as the square of the
distance between the object and the eye. In other words, the closer
the object, the stronger the reflected light.
2. Contrast
Contrast is simply the difference in brightness of an object and its
background. Distinct contrast allows the brain to differentiate easily
between areas of strong and mild visual stimulation. For example,
black words on white paper are read easily, but gray lettering on a
slightly lighter gray paper is much harder to interpret.
3. Luminance
Luminance, simply put, is the brightness of an object, or the strength
of the light reflected from it. The greater the luminance, the stronger
the visual stimulation, and the easier the object is to see.
4. Time
Time refers to how long it takes to see an object clearly. Under the
best conditions, it takes slightly less than one-sixteenth of a second
for the eye to register an image. In a dim setting, it takes longer.
This is especially important where motion is involved, such as in
night driving.
Obviously, the luminance of an object, or the quantity of light
reflected from it, determines the level of visual stimulation the
object provides. Now it is time to look more closely at the mechan-
ics of light quantity, and also to investigate another factor that
influences visual acuity, namely, light quality.
8 The Lit Interior

Light quantity
In evaluating light quantity, it will be helpful to examine the afore-
mentioned inverse square law, and some of the nomenclature that
is used to describe the features of light. Succinctly put, the inverse
square law as applied to lighting states that: ‘the luminance of an
object is directly proportional to the light output of the illuminat-
ing source, and inversely proportional to the square of the distance
between the source and the object’. At the risk of losing a few of
you to the geometry, let’s look at Figure 1.8, which graphically illus-
trates the inverse square law.
Light output from a source is normally expressed in candlepower,
and light output in a given direction is expressed in candelas. The
density of light flux radiating from the source is expressed in
lumens, and the luminance, or light reflected from an object is
expressed in footcandles. Footcandles has units of lumens per
square foot. Figure 1.8 shows a point source of uniform candle-
power, having 100 candela in all directions. If we approximate
light propagation in a solid angle of 1 steradian and go out a
distance of 1 foot from the source, we see that the angle circum-
scribes an area of 1 square foot. The glossary defines a lumen as
the flux density generated within 1 steradian by a point source of
1 candela. We have 100 candela in the source of Figure 1.8, so the
flux density will be 100 lumens. Using the lumens per square foot
definition, we see that the luminance at 1 foot will be 100/1, or
100 footcandles (100 fc). If we go out 2 feet from the source, we
see that the area circumscribed by the steradian envelope is now
2 squared, or 4 square feet. Similarly, at 3 feet, the area is 9 square
The design medium 9
Figure 1.8. Inverse square law (source: F.H. Jones).

feet. Corresponding luminances are 100/4, or 25 fc, and 100/9, or
11 fc, respectively. For the mathematicians among you, this
relationship can be expressed mathematically as I = L/D2
, where I
is illumination in footcandles, L is the luminance of the source in
lumens, and D2
is the square of the distance in feet from the source
to the point under examination.
The inverse square law works pretty well in predicting the illumi-
nation on a surface from a point source directly above the surface,
but what happens when we want to predict the effects of a source
that is at an angle to the surface under consideration? We can use
an old static mechanics trick and expand the inverse square law to
take care of the angle by breaking the angle down into its two
components, one parallel to and one normal to the surface, and
then discarding the parallel component. Figure 1.9a illustrates this
graphically.
Now, if you’ve ever had a statics course, you’ll remember that a
force applied to a Point P on a beam at an angle ␻ from the normal
is treated this way, and that the downward component of the force
is equal to the total force times the cosine of ␻. If you’ve never had
statics, no matter, it still works that way. Taking luminance L as
the ‘force’ of the light, and using the inverse square law, we can
say that the illumination I on a point from a source that is at an
angle X from being directly above the point, and at a distance D
from the point is: I = L cos X/D2
. This is called the cosine law of
incidence. To get some idea of what this means, look at the light
sources above you and all around you. All of these contribute to
10 The Lit Interior
Figure 1.9. Two-component force vector.
(a) (b)

the total illumination falling on your desktop. If you have a good
calculator, and about a month of free time, you can calculate
exactly what that illumination is, using this equation.
Fortunately, we don’t have to get bogged down in extensive,
tedious calculations of this sort. As we will see in a later chapter,
there are plenty of good computer programs out there to perform
these calculations for you. It is, however, helpful to know the logic
behind the calculations, so that you will be able differentiate
between valid output and computer-generated gibberish.
So there you have the factors involved in the quantity of light
that illuminates a chosen area. To review in a nutshell, these are
the strength in candlepower of the illuminating sources; the distance
those sources are from the area; and the angle those sources are
from the normal to the surface of the area. Adequate quantity of
light, however, doesn’t always insure good visibility. The quality of
the light is often as important as the quantity.
Light quality
What do we mean by light quality, and what are the factors which
contribute to ‘good’ or ‘bad’ quality illumination? Simply put, good
quality illumination is that which provides a high level of visual
comfort, and allows us to view tasks clearly and easily. This affects
our psyche in a positive way. On the other hand, poor visual comfort
illumination irritates us. The four most important factors affecting
visual comfort are glare, brightness ratio, diffusion, and color rendi-
tion. Let’s look now at each of these factors in greater detail.
Glare
We’ve all experienced glare in our everyday lives: bright lighting
fixtures located in your field of view, or sunlight coming through
a window. This is known as discomfort glare, and the degree of
discomfort inflicted depends on the number, size, position, and
luminance of the glare sources. In interior lighting design, we are
primarily concerned with discomfort glare from windows and
overhead lighting fixtures. Other forms of glare are disability glare
and veiling reflections. Disability glare obliterates task contrast, and
scatters the light within your eye to the point that visibility is
reduced to zero. A common example is glare from a glossy
magazine page that makes it impossible to read the page. Veiling
reflections, such as lighting fixture ‘images’ on your computer
monitor, make it hard to see what is on the screen. The severity of
The design medium 11

glare in any form is primarily dependent on two factors: the bright-
ness and position of the source.
Brightness ratio
The brightness ratio is the brightness contrast between the task and
the background. This affects the amount of work our eyes have to
do in order for us to perform the task. For example, a high bright-
ness task in a low brightness surrounding forces the eye to contin-
ually adjust from one light level to the other. Conversely, a low
brightness task surrounded by a bright background tends to obscure
contrast, and the eye tends to be attracted away from the task.
Obviously, a balance between task and background brightness is
desirable for effective viewing.
Diffusion
Contrary to the above factors, which affect viewing negatively,
diffusion generally improves visual comfort. Diffusion results from
light arriving at the task from many different directions. A highly
diffuse lighting system will produce no penumbra, or sharply
defined shadows. Diffuse lighting is desirable in office areas where
computers are in use, in school classrooms, and in library reading
areas. Diffuse lighting is accomplished through the use of many low
brightness fixtures, or through the use of indirect lighting, where
the light is reflected from diffuse surfaces, such as a white ceiling,
before reaching the task.
Color rendition
Color of light affects the ‘mood’, or emotional aspects of a space.
It also affects the accuracy with which we perform tasks. We’ve all,
at one time or another, purchased a garment under artificial light-
ing, only to have it change color when we got it out into the
sunlight. That happens because the artificial light source does not
contain the full visible spectrum of colors, as does the sunlight. As
noted before with the blue ball example, we see only those colors
which are reflected from a surface. Obviously, those tasks that
involve color discrimination should be lighted by a source that
contains as much of the visible spectrum as possible. In other situa-
tions, the mood of the environment can be altered by the use of
‘warm’ or ‘cool’ colors, high in reds, or blues, respectively.
Unlike light quantity, light quality is subjective in nature, and is
not easy to calculate by mathematical formulae. The lighting indus-
12 The Lit Interior

try has, however, come up with several methods that the designer
can use to evaluate the relative quality of lighting systems. The first
of these is equivalent sphere illumination (ESI). This is a complicated
method of relating illumination of a task on a surface within the
design space to that of a task on a surface in the center of a sphere
that is equally illuminated throughout. The logic being that the
lighted sphere will provide the optimum illumination, and that the
space should be designed to match the footcandle requirement of the
sphere as closely as possible. For example, if a task requiring 100 fc
in the design space was put into the sphere, and the lighting level
was adjusted to provide the same task visibility, and that level was
60 fc, then the ESI would be 60 fc. Equivalent sphere illumination
takes into account room geometry and reflectance, fixture charac-
teristics, and viewer position. Needless to say, only fixture manufac-
turers with big computers attempt ESI calculations. Another
comparison type system evaluator is the relative visual performance
(RVP) factor, which is expressed in percentages. The RVP represents
the percentage likelihood that a standardized visual task can be
performed within the designed lighting system. Age of the viewer,
luminance and contrast are all included in RVP calculations. When
comparing systems, the one with the higher RVP will provide better
light quality. Also expressed in percentages is the visual comfort
probability (VCP), which is the percent of viewers positioned in a
specific location, viewing in a specific direction, who would find the
lighting system acceptable in terms of discomfort glare. Visual
comfort probability takes into account room geometry and
reflectances, fixture number, type and luminance. As with RVP, the
higher the VCP, the better the light quality of the installation.
The lighting industry has done a yeoman’s job of trying to
quantify the factors of light quality so that the above evaluators
may be calculated numerically. There are so many non-direct factors
involved, however, that these calculations are best left to fixture
manufacturers with plenty of time and people, and large comput-
ers. Most fixture manufacturers publish some sort of visual comfort
data for their fixtures. A good lighting designer is aware of the
causes of visual discomfort, and develops an innate ‘feel’ for which
fixtures will perform well where, rather than trying to rely solely
on numbers and calculations to provide good light quality.
The psychology of lighting
A seasoned lighting designer can visualize how a given lighting
system will look and perform within a space. He also can predict

how an observer will react to the system. This insight is gained with
experience, of course, but certain basic relationships of light and
space and the psyche are always present, and are worth mention-
ing. The first is the location of the plane of brightness, or the bright-
est surface in the space. Figure 1.10 illustrates some different planes
of brightness.
A ceiling left in shadow creates a secure, intimate, and relaxing
‘cave’ environment suitable for lounges and casual dining. High
brightness on the ceiling creates the bright, efficient, working
atmosphere desirable for offices, classrooms, and kitchens. Bright-
ness on the vertical planes draws attention to the walls and expands
the space visually, and is appropriate for art galleries, merchandis-
ing, and lobbies. Such facilities often also use variations of light
intensity on the walls to accentuate a desired feature.
Variations of light intensity form areas of light and shadow,
which are desirable if you are trying to create a ‘mood’ environ-
ment, rather than an evenly illuminated workplace. The interplay
of light and shadow add variety to a space, and provide visual relief
to an otherwise monotonous environment. Scallops on a wall from
downlights, shadows on the ceiling from uplights, or highlights
from accent lighting create areas of visual interest, and can draw
attention to a desired area or object. The designer must be careful
not to overdo it, though, because too many lighting effects in one
space have roughly the same visual effect that too many sidebars,
colors, and font styles do to a magazine page: the original design
intent is obscured or obliterated.
It is always best to work with the architect from the outset of a
project to get in tune with the flavor or mood that he or she is
trying to create in a space. Architectural features can be modeled
through the use of shadows, as can objects within the space. A
three-dimensional object lighted directly from in front will appear
14 The Lit Interior
Figure 1.10. Planes of brightness (source: F.H. Jones).

flat, but when lighted from an angle, will assume depth and round-
ness. We all remember the ‘Frankenstein flash’ from photography
class, where the hand-held flash is placed beneath the chin of the
subject. The resulting photo looks like a Boris Karloff publicity
shot. This happens because of the striking contrast between the
brightly lit and deeply shadowed facial features. The same effect
can be achieved in architectural spaces through the use of uplights,
downlights, and lighting from the side. Figure 1.11 illustrates
modeling through the use of shadows.
Areas of brightness can also be used to create mood, or accent
architectural features. Small pinpoints of brightness from tiny lamps
or reflections add sparkle and glitter to a space, which enhances
the gaiety, elegance, and festivity of the space. You can try this
yourself at home with a string of clear Christmas mini-lights. Wrap
that ficus tree in the corner with the lights, and plug them in. Note
the overall effect. Or string the lights around an architectural
feature, such as an arched doorway. You’ll get the idea. The watch-
word here is the same as with light and shadow, don’t overdo it –
and keep some background light. Without sufficient background
Figure 1.11. Effects of shadows (source: F.H. Jones).

lighting to soften the contrast, glitter can become glare. The light-
ing is used to accent the architecture – not overpower it. Figure
1.12 shows an effective use of sparkle and glitter.
Summary
We now know the nature of light, how the eye responds to light,
and how light behaves when subjected to various control mediums.
We’ve also explored methods for quantifying the intensity of light,
16 The Lit Interior
Figure 1.12. Sparkle and glitter (source: F.H. Jones).

and some methods for assessing the visual comfort of a lighting
system. All of this knowledge will come into play in every lighting
system that you design.
We have also looked at some of the artistic aspects of lighting
design. Although these will probably not be a majority of your total
design effort (unless you specialize in artistic lighting design), this
is where you can use your creativity to create your own unique
lighted environment.
In the next chapter we will explore some of the tools that you
have at your disposal for creating a lighting system. But first, let’s
see how much you’ve retained from this chapter. . .
Exercises
1. What is the wavelength range of the visible portion of the
electromagnetic spectrum?
2. Which light rays contain the most energy?
a. Ultraviolet
b. Infrared
c. Blue–Green
3. When we see an object, we are actually seeing
a. Light striking the object
b. Light reflected from the object
c. Light being diffracted by the object
4. We see colors by using the eye’s
a. Rods
b. Cones
c. Iris
5. What are four things that happen to our eyes as we age?
6. Name four ways that a light ray can be modified.
7. What is the purpose of a lens?
8. What are the three types of reflection?
9. What are the most important factors determining the visibility
of an object?
10. In 31 words or less, parrot back the definition of the inverse
square law as it applies to lighting.
11. Problem: A point source of 200 lumens, located directly above
a surface, and 2 feet from it, will produce how many footcan-
dles on the surface?
12. What law would we invoke to calculate illumination by a
source at an angle from the normal to the lighted surface?
13. What is considered ‘good quality’ illumination?
14. What is disability glare? Why do we call it that?

15. What determines brightness ratio?
16. Where would diffuse lighting be used?
17. What determines the perceived color of an object?
18. What does a visual comfort probability (VCP) of 70 tell us
about a lighting system?
19. Which ceiling brightness would we try to obtain in an upscale
dining space?
a. High
b. Medium
c. Low
20. True or false: To add spice to a space, we always try to use as
many lighting effects as the budget will allow.
21. What methods would you use to achieve effective shadows?
18 The Lit Interior

Just as an artist has paints and canvas, and a sculptor has chisels
and marble, a lighting designer has certain tools with which to create
a lighted environment. There is a wide variety of lighting sources,
or lamps, available to provide the desired light intensity and color,
and there is an almost unlimited choice of lighting fixtures (called
luminaires from here on out) to shape and place the light in just the
right pattern, and there is a multitude of control systems to make
those luminaires behave as the designer intends. Like the artist,
whose canvas has finite limits, the lighting designer has energy, task,
and code requirements that establish the boundaries of the design.
To aid in meeting these requirements, the designer has several calcu-
lation techniques, both manual and computerized, available to help
predict the adequacy and long-term performance of the design.
As with any endeavor, the lighting designer will develop skill and
technique with experience. Until that experience is gained, there are
a number of ‘tried and true’ universal lighting techniques that may
be used to solve a variety of design problems. Some of these
techniques are included in this chapter.
Understanding this powerful arsenal of tools will enable the
designer to specify a superior lighting system for any space with
confidence, be it a warehouse or a specialty retail shop.
Let’s now take a closer look at these tools.
Lamps – the light source
Lamp theory
Artificial light, meaning something other than sunlight, may be
produced either chemically, mechanically, or electrically. Chemical
light is used for very special applications, such as the emergency
wands that you see in sporting goods stores; mechanical (flame –
2 The design tools

gas lamps) is primarily used to create atmosphere. By far, the great-
est producer of usable artificial light is electricity. The electrically
driven light source is what we will examine here.
The two most important methods by which we can produce light
from electricity are incandescence and photoluminescence. These
are big words used to describe the processes by which the lamps
that we use every day produce light. Let’s see how each of these
processes works.
Incandescence
Incandescence is the visible radiation produced by a body at a high
temperature. In incandescent lamps, the temperature is created by
passing an electric current through a wire filament which has a
finite resistance to current flow. The result is called Joule heating,
and is proportional to the resistance of the filament, and to the
square of the current flowing. As the filament gets hot, it glows,
first red, and then white. The white light produced by a glowing
filament contains all of the colors of the visible spectrum to some
degree, and therefore produces a continuous spectrum of light. In
incandescence this spectrum is higher in intensity toward the longer
wavelengths, or the ‘red’ end of the visible spectrum, but the actual
intensities of the various wavelengths depend upon the temperature
of the filament. Figure 2.1 shows the spectral energy distribution
of a tungsten filament at 3000 K.
20 The Lit Interior
Figure 2.1. Spectral distribution of a tungsten filament at 3000 K (source: Osram/Sylvania).

Photoluminescence
Photoluminescence is what happens when neutral gas atoms collide
with electrons in an electric arc discharge. Some of the energy of
the collision is released as visible radiation, and some as ultravio-
let (UV) radiation with wavelengths below the visible spectrum. The
energy is released at specific wavelengths which are dependent on
the chemical makeup of the gas. The resulting spectral distribution
is a discontinuous series of ‘spikes’, rather than the smooth distri-
bution curve of the incandescent source. This is illustrated in Figure
2.2, which is the spectral energy distribution for a mercury vapor
lamp.
Figures 2.1 and 2.2 are what is called spectral energy distribution
curves. They show what wavelengths, and hence what colors of light
are produced by the source under examination. These curves are a
good indicator of the color-rendering abilities of the source.
Remember the blue ball example from Chapter 1? OK, let’s assume
that the color of the ball is about 440 nanometers in wavelength.
The design tools 21
Figure 2.2. Spectral distribution of a clear mercury vapor lamp (source:
Westinghouse).

What would the ball look like if it were illuminated by the mercury
vapor source in Figure 2.2? Since the ball’s color is contained in the
spectrum of the source, the ball will reflect the 440 nanometer
wavelength light, and appear . . . bright blue. What would a red ball
of 700 nanometers wavelength look like? Right – brownish-black!
Since very little 650 nanometers wavelength light is in the mercury
vapor spectrum, the ball will absorb almost everything. Now you
know why meat markets don’t use mercury vapor lamps.
Color temperature
It is common to speak of ‘cool’ colors such as blue and green, and
‘warm’ colors, such as red and orange. These colors, of course, are
the result of the spectral distribution of the light source illuminat-
ing them. Light sources, then, can be called cool or warm, or in-
between, dependent upon their spectral distribution. Lighting
designers find it useful to be able to assign temperature numbers to
define the degree of coolness or warmth of a source.
In correlating color to temperature, it is helpful to think of the
old time blacksmith heating a piece of iron. As the iron started to
heat up, it would glow a deep red. As it got hotter, it would become
bright red, and finally, white hot. The easiest way to describe the
color of the glowing metal was to give its temperature, because any
two glowing pieces of the same metal having the same temperature
would always have the same color.
The tungsten of an incandescent lamp filament behaves in the
same way, and the color of its emitted light is always directly
related to its temperature in Kelvin degrees. The whiter the light,
the higher the temperature. The color temperature of a household
incandescent lamp, for example, is a little less than 3000 K. Strictly
speaking, color temperature applies only to incandescent sources
and to natural sources such as the sun and the sky.
When it comes to photoluminescent sources such as fluorescent
and gaseous discharge lamps, the correct term to use is correlated
color temperature. When a fluorescent lamp is said to have a corre-
lated color temperature of 3000 K, that means that its color looks
more like that of a 3000 K incandescent source than that of an
incandescent source of any other temperature. This does not mean
that it will illuminate colored objects the same way a 3000 K incan-
descent source will, however. Figure 2.3 shows the spectral energy
distribution curves for several popular fluorescent lamps.
As shown in Figure 2.3, fluorescent lamps do not have the
smooth continuous output curve of an incandescent lamp, so its
color temperature is only an apparent one. Figure 2.3 illustrates
22 The Lit Interior

that two 4100 K fluorescent lamps can have very different spectral
distributions. In fact, with the right mix of phosphors, it would be
possible to make a fluorescent lamp that had most of its output in
only two narrow peaks of light, one blue and one yellow, and
balance the colors so that the lamp had a correlated color temper-
ature of around 3000 K. The color performance of the lamp would
be very poor, however. A red object would appear brown under this
lamp, while it would appear normal under a 3000 K fluorescent
source with an spectral distribution containing reds.
Color rendering index
Lamp manufacturers, as well as lighting designers, find it useful to
be able to compare how well the different sources render colors, so
in 1965 an international panel of experts, the Commission Interna-
tionale de la Eclairage (CIE) devised an extremely complicated
The design tools 23
Figure 2.3. Spectral distribution of fluorescent lamps (source: F.H. Jones).

method of testing to assign a color rendering index (CRI) number to
each lamp on the market. Fortunately, doing the mathematics falls to
the manufacturer, and all the designer has to remember is that the
higher the CRI, on a scale of 0–100, the better that lamp will render
colors. Figure 2.3 lists the CRI for each lamp shown. It is seen that
lamps of the same color temperature can have very different CRI
ratings, depending on the colors contained in its spectral distribution.
In general, the higher the CRI, the better a fluorescent or
discharge source compares with a natural source at the same corre-
lated color temperature. It has been said that correlated color
temperature is what the lamp is trying to be, and its color render-
ing index shows how well it is succeeding.
Lamp manufacturers have devoted large amounts of time and
money to developing exotic phosphor coatings for the inside of
photoluminescent lamps in order to improve CRI. As a result, some
fluorescent lamps with a CRI of over 90 are readily available.
Let’s take a closer look now at the three major types of light
sources, or lamps, which you, as a lighting designer, will use. These
are incandescent, fluorescent, and high intensity discharge (HID)
lamps.
Lamps – major types
Incandescent lamps
Standard incandescent lamps
The standard incandescent lamp is the oldest electric lighting
technology still available today. Although relatively short lived
(750–3000 hours), and fairly inefficient (6–24 lumens per watt),
incandescent lamps are widely used in residential and other appli-
cations. This is primarily because they are cheap, easy to obtain,
work in inexpensive fixtures, have good color rendition, and
perform well in low ambient temperatures. Standard incandescent
lamps are still constructed today much the same way they were
when they were originally introduced: two lead-in wires are
attached to a metal screw base, and are insulated from each other
by a glass stem. A tungsten filament is attached between the two
lead-in wires, and a glass envelope, called the bulb, surrounds the
filament structure and is attached to the base. The bulb is evacu-
ated, then filled with an inert gas to prevent the filament from
burning up. The envelope may be frosted to diffuse the light emitted
from the filament. Figure 2.4 illustrates the construction of the
incandescent lamp.
24 The Lit Interior

In operation, electric current is passed through the filament,
which heats up, and produces visible light. The amount of current
flowing in the filament determines the brightness and the color of
the lamp, from dull red to bright white. An incandescent lamp is
easily dimmed by simply reducing the current through the lamp.
This is easy to accomplish using a rheostat, or variable resistor, in
the lamp circuit.
As you can see from Figure 2.1, the light produced by a tungsten
filament is strongest in the long wavelengths, or red region, of the
visible spectrum. Incandescent sources can therefore be considered
The design tools 25
Figure 2.4. Incandescent lamp construction (source: Osram/Sylvania).

‘warm’ sources, because reflection from an object will be strongest
in the red region.
Standard incandescent lamps are manufactured in a large variety
of shapes and sizes. Figure 2.5 shows some of the more common
ones.
Each shape of incandescent lamp is assigned a letter, or letters,
and each size is assigned a number. The letters loosely describe the
lamp, and the number tells the diameter of the lamp in eighths of
an inch. For example, the A-19 lamp in Figure 2.5 is of Arbitrary
(or Apple) shape, and is 19/8, or 2 3/8 in. (6 cm) in diameter. Some
combinations describe the function of the lamp as well as the size,
like the PAR-38, which has a parabolic aluminized reflector
coating inside the glass envelope, and can be bought in either flood
or spot light configuration. It is 38/8, or 4 3/4 in. (12 cm) in
diameter.
In the years since the invention of the incandescent lamp, lamp
manufacturers have done extensive R & D to improve the life and
the lumen output of the lamps. This work has been directed toward
both the envelope and the gas which fills the envelope.
Tungsten halogen lamps
The tungsten halogen lamp is one result of this effort. The
halogen fill gas prevents the lamp envelope from darkening as
26 The Lit Interior
Figure 2.5. Incandescent lamp shapes (source: Osram/Sylvania).

the lamp ages by carrying vaporized tungsten back to the
filament, so more light is produced, and the life of the lamp is
extended. The envelope itself is small, and made of quartz,
instead of glass like regular incandescent lamps. This combina-
tion allows the tungsten halogen lamp to operate at a much
higher temperature than a standard incandescent lamp, resulting
in a higher efficacy, or lumen per watt, output. Since the lamp
is hotter than a standard incandescent, the light output is whiter,
and the color rendition is more evenly balanced than the red-rich
output of the standard lamp. Tungsten halogen lamps operate
with a color temperature of 3000–3300 K and have a CRI of
100. Two types of tungsten halogen lamps are available: the line
voltage; and the low voltage lamp, and each type is available in
a variety of shapes and sizes.
Infrared reflecting lamps
One version of the tungsten halogen lamp, the infrared (IR)
reflecting lamp, uses a dichroic coating that reflects infrared back
into the lamp, and passes visible light as output. This serves two
functions: it reduces the lamp’s energy wastage to heat; and it
helps to heat the filament to a higher temperature. A variation of
this coating is used in the low voltage MR-16 lamp to produce a
‘cool’ brilliant white light beam. This lamp gets extremely hot,
and cannot be used in an indoor luminaire without protective
shielding.
Incandescent lamp benefits
Some of the more prominent benefits of incandescent lamps are:
1. inexpensive;
2. high CRI (good color rendition);
3. operates in inexpensive fixtures;
4. easily dimmed;
5. instant on–off;
6. insensitive to ambient temperature;
7. available with a variety of built-in reflectors;
8. available in many wattage and colors.
Incandescent lamp drawbacks
Some of the drawbacks of incandescent lamps are:
1. short life (750–3000 hours);
2. poor over-voltage tolerance;
3. low lumen output per input watt (efficacy);
4. high heat generation (90% of input wattage goes to heat).
The design tools 27

Incandescent lamp uses
Incandescent lamps are generally best suited for use in:
1. dimmable systems;
2. accent and specialty retail lighting;
3. outdoor convenience and decorative lighting systems;
4. mood lighting.
Fluorescent lamps
Fluorescent lamps are the most commonly used commercial light
source in the US, and perhaps the world. In the US, about 75% of
the commercial space is illuminated by a fluorescent source. This is
because fluorescent lamps are relatively cheap, long lived, have a
high light output to watts input ratio (efficacy), and are designed
for use in fixtures which fit into the architectural schemes of
commercial structures.
Let’s look at how a fluorescent lamp is built, and see how it
operates.
Fluorescent lamps are built using a tubular glass envelope coated
on the inside with a mix of phosphors. Inert gas and a small
amount of mercury is introduced into the tube to provide the atoms
for photoluminescence. The tube is slightly pressurized, and the
ends of the tube are capped with electrodes, which contain a
cathode to generate an arc.
In operation, when the arc is struck between the electrodes at
each end of the tube, the mercury vaporizes, and the electric arc
colliding with the atoms of mercury vapor produces UV light along
the length of the tube. This high-energy light strikes the phosphor
coating, and imparts energy to it, which causes the phosphor to
fluoresce, or produce light. The chemical makeup of the phosphor
compound determines the color of the light produced.
If this process were allowed to go unchecked, the current flow
in the arc would continue to increase until the lamp overheated and
destroyed itself. To regulate the current flow, a ballast transformer
must be used in conjunction with the lamp. The ballast transformer
also serves to start the arc in instant start lamps, and to provide
coil voltage in rapid start lamps. Since it must generate higher
voltages, the ballast transformer used with instant start lamps is
larger than that used with rapid start lamps. A larger ballast is also
used for the high output (HO) and very high output (VHO) lamps,
which are constructed to allow a larger current flow in the arc.
Fluorescent lamps are available in correlated color temperatures
of 2700 K, which approximates incandescent lighting, all the way
28 The Lit Interior

up to 6500 K, which approximates daylight. The lower tempera-
ture lamps, up to 3400 K, are said to be ‘warm’ lamps; the mid-
range lamps, from 3500 to 4000 K, are considered ‘natural’, neither
warm nor cool; and lamps having temperatures of 4100 K and
above, are called ‘cool’ in color. The lamps are available in color
rendering indices (CRI) from 57 to above 90. In general, the higher
the CRI, the more expensive the lamp.
The two most popular types of fluorescent lamps, the rapid start
and the instant start, utilize different methods of arc starting.
Rapid start fluorescent lamps
The rapid start lamp uses a cathode consisting of a coiled
tungsten wire coated with an emission material. When voltage is
applied across the coil, it heats up, and the coating emits
electrons. These electrons produce an arc in the inert gas. This
type of lamp necessarily has two pins in each electrode to power
the coil.
Instant start fluorescent lamps
The instant start lamp uses a ballast transformer to boost the
voltage up to a sufficiently high level to strike the arc directly. This
only requires a single pin in each electrode, although many lamp
manufacturers use the two-pin configuration, and connect the pins
together. Figure 2.6 shows the components of the rapid start
fluorescent lamp.
The design tools 29
Figure 2.6. Fluorescent lamp construction (source: Osram/Sylvania).

High output and very high output fluorescent lamps
High output (HO) and very high output (VHO) fluorescent lamps
are constructed in the same manner as standard fluorescent lamps,
except that heavier components are used to allow higher than
normal current flow within the arc. As a result of this higher
current flow, the arc–electron collisions are more violent, and the
lamp produces more lumens than a standard lamp. The cost of this
extra output is the increased energy required to operate the lamp.
This cost is often justified if higher mounting heights are required
by the application.
Compact fluorescent lamps
Compact fluorescent lamps have the same components, and operate
the same way that the large tubular lamps do. The glass envelopes
of the compact lamps are usually bent into a ‘U’ shape to offer
more surface area in a small space. There are compact fluorescent
lamps available that will serve as low-energy substitutes for incan-
descent lamps in all applications up to about 150 W. The general
rule of thumb is that 1 input watt of compact fluorescent energy
produces as much light output as 4 input watts of incandescent
energy.
Other fluorescent lamps
There are also fluorescent lamps available which have no
electrodes, but instead control the arc through inductive
coupling. The Osram–Sylvania ‘Icetron’™ is one such lamp. Since
there are no electrodes to deteriorate, these lamps have an
extremely long life – about 100 000 hours on average. These
lamps are relatively expensive, and are used primarily where
lamp replacement is difficult, for example, in a theater with 40
foot (12 m) high ceilings.
Fluorescent lamps are described in the manufacturer’s litera-
ture in much the same way that incandescent lamps are: the first
letter in their designator is either ‘F’, for fluorescent, or ‘CF’ for
compact fluorescent. The second letter in the designator is used
to describe manufacturer’s information about the lamp. For
example, ‘FB’ would describe a U-shaped, or ‘bent’ tube. One
lamp manufacturer, Osram–Sylvania calls their T8 energy saving
lamps ‘Octron’, so the designator would be ‘FO’ for a Sylvania
T8 lamp. Absence of a letter in this position indicates a standard
lamp. The first number in the designator is usually the wattage
of the lamp, with a few exceptions: the number ‘48’ is sometimes
used to indicate a 4 ft, or 48 in. (1.2 m), long tube, and ‘96’ is
used the same way for an 8 ft (2.4 m) long tube. Following the
30 The Lit Interior

wattage number is the shape letter descriptor, usually ‘T’, for
tubular. Following the shape descriptor is a number which is the
diameter of the tube in eighths of an inch, and that completes
the basic lamp designator. For example, an F32T8 lamp would
be a fluorescent 32 W tube, 1 in. (2.5 cm) in diameter, under-
stood to be standard, or 4 ft (1.2 m) long. Following the basic
designator, and separated from it by a forward slash (/) are CRI
and color descriptors, as well as manufacturers’ specialty descrip-
tors. For example, F32T8/841 denotes the above 32 W lamp,
with a CRI of 80 or above, and 4100 K in color. High output
and very high output lamps are designated with the suffix HO
or VHO, respectively.
Fluorescent lamp advantages
Some of the advantages of fluorescent lighting are:
1. long life (20 000 hours average);
2. low cost;
3. high lumen to input watt ratio (F32T8/841 has efficacy of about
8 times that of standard incandescent);
4. available in a wide range of sizes and colors;
5. available with high CRI ratings;
6. low heat generation.
Fluorescent lamp drawbacks
Some of the drawbacks associated with fluorescent lighting are:
1. temperature sensitive. Output drops drastically in low temper-
atures. Lamps used outdoors require special low temperature
ballasts;
2. require expensive dimming ballast for dimming;
3. lamps contain mercury, which is classified as an environmental
hazard, and can present difficulties in disposal of burned out
lamps;
4. can produce stroboscopic effect around rotating machinery,
since the arc turns off and on at twice the frequency of the
incoming power with magnetic ballasts.
Fluorescent lamp uses
Fluorescent lamps should be the first choice for:
1. office space ambient lighting;
2. large retail space ambient lighting;
3. interior common space lighting;
4. compact fluorescent lamps should be used in recessed
downlighting and accent lighting for energy savings.
The design tools 31

High intensity discharge (HID) lamps
High intensity discharge (HID) lamps operate on the photolumines-
cence principle like fluorescent lamps. That is, they require an
electric arc passing through, and colliding with gas atoms to produce
light. However, unlike fluorescent lamps, which produce 90% of
their light from phosphors excited by the generated light, most of
the light produced by HID lamps is the arc-generated light itself.
This requires that the HID lamps operate at a higher tempera-
ture, with a much higher intensity arc, and under a much higher
pressure than fluorescent lamps. To do this, the HID lamp has an
inner pressurized tube, called the arc tube, where the high intensity
arc takes place, and an outer envelope to protect the arc tube. Like
the fluorescent tube, this outer envelope can be coated with
phosphors to improve the CRI of the lamp. The space between the
outer envelope and the arc tube is evacuated to a high degree to
maintain a constant temperature in the arc tube. High intensity
discharge lamps utilize a starting electrode to ionize the gas mixture
and start the arc, and a coated filament coil electrode in each end
of the arc tube to maintain the arc. Like the fluorescent lamp, the
HID lamp must be used in conjunction with a ballast to provide
starting voltage, and to regulate the current flow once the arc has
started. The ballast must be closely matched to the lamp for the
system to operate properly. High intensity discharge ballasts are
sensitive to momentary drops in input voltage, and for some
ballasts, a drop of greater than 10% will extinguish the lamp.
Figure 2.7 shows the construction of typical HID lamps.
The high intensity arc in an HID lamp will not strike until the
lamp comes up to operating temperature, so there is an average
warm-up time of 2–6 minutes from the time the switch is thrown
until the lamp reaches full output. Conversely, if the lamp is turned
off for any reason, the gasses inside the arc tube will be too hot to
re-ionize immediately, and there will be a cool-down period of 5–15
minutes before the arc can be restruck. Table 2.1 is a comparison
chart which shows the warm-up and restrike times for the various
HID sources.
Despite these drawbacks, HID lamps are among the most
efficient and long-lived lamps in use today. They are widely used
to light large, high ceiling spaces, such as warehouses or gymnasi-
ums. Included in the HID family of lamps are mercury vapor, metal
halide, and high pressure sodium. A close cousin, the low pressure
sodium lamp, will also be included in the HID group even though
it operates at a lower arc tube pressure than the others.
Let’s look now at the characteristics of each of these lamps.
32 The Lit Interior

The design tools 33
Figure 2.7. High intensity discharge (HID) lamp construction (source: Philips Lighting).
Mercury Vapor
Metal Halide
High Pressure Sodium

Mercury vapor lamps
Mercury vapor lamps produce the color spectrum of mercury,
which appears as a series of ‘spikes’ on the spectral distribution
charts. The distribution for a clear mercury vapor lamp was shown
in Figure 2.2.
Looking back at Figure 2.2, it can be seen that a large portion
of the distribution is in the UV region, which is harmful to both
the eyes and the skin. To counteract this, the outer envelope of the
mercury vapor lamp is coated with a UV inhibitor. Even with the
inhibitor, the clear mercury vapor lamp still produces light with a
correlated color temperature from 5600 to 6400 K. In addition,
there are a lot of colors that are not included in the spectrum of
the lamp. This leaves the lamp with a CRI of less than 20, which
offers very poor color rendering, particularly in the yellow–red
region. To correct this, manufacturers have formulated phosphor
coatings for the outer envelope which fluoresce in those colors that
the mercury gas lacks. Two of the resulting lamps are the ‘warm’
mercury vapor lamp with correlated color of about 3300 K, and a
‘white’ lamp at about 4100 K. These lamps have a CRI of 50 or
more, which is not great, but is a big color improvement over the
clear lamp.
Mercury vapor lamps are the least efficient of all the HID lamps,
having a lumens per input watt ratio (efficacy) lower than some of
the fluorescent lamps. Mercury vapor lamps are, however, long
lived, having an average life in excess of 24 000 hours. Mercury
vapor lamps come in a number of shapes and sizes, including reflec-
tor lamps. The ballasts must be closely matched with the lamp in
a mercury vapor system.
In the US, The American National Standards Institute (ANSI) has
assigned a manufacturer’s designator for mercury vapor lamps of
‘H’, taken from the chemical designation Hg for mercury, which (to
throw in a little more useless trivia) comes from the Greek word
‘hydrargyrum’. Therefore, the first letter in a mercury vapor lamp
designator is H. The following numbers indicate the ballast required
for use with the lamp; the two letters following the numbers
34 The Lit Interior
Table 2.1. High intensity discharge warm-up and restrike times.
Light source Warm-up time Restrike time
Mercury vapor 5–7 min 3–6 min
Metal halide 2–5 min 10–20 min
Pulse start metal halide 2–3 min 3–4 min
High pressure sodium 3–4 min 1–2 min
Low pressure sodium 7–10 min 3–12 s

indicate the physical characteristics of the lamp (i.e., size, shape,
etc.). This is separated by a dash from another number, which is
the wattage of the lamp. Letters following a forward slash after the
wattage indicate manufacturer specialty features. Thus, an H38AV-
100/DX lamp is a 100 W mercury vapor lamp requiring a type 38
ballast, having size and shape code AV and a Deluxe white
phosphor coating.
Some of the beneficial features of mercury vapor lamps are:
1. long life (24 000+ hours);
2. blue–green output flattering to plant color;
3. available in a variety of sizes and shapes;
4. least expensive HID source.
Some of the drawbacks to mercury vapor lamps are:
1. long warm up time to full output (3–5 minutes);
2. poor CRI, even with phosphor coating;
3. inefficient – lowest lumen-per-watt ratio of all the HID lamps;
4. produces UV radiation which can cause skin and eye burn if
the outer envelope is broken – must be shielded for indoor use.
Mercury vapor lamps are best suited for landscape or atrium light-
ing, where the color and long life are an asset.
Metal halide lamps
Metal halide lamps are a very efficient source of ‘white’ light, and
are available in wide wattage range. The efficacy, or lumen output
per watt input ratio for metal halide is 3–4 times that of mercury
vapor, and exceeds that of fluorescent above 400 W. Metal halide
also has a relatively high color rendering index, with an average CRI
of about 70, and some lamps are available with a CRI above 80.
Metal halide lamps come in sizes from 50 to 2000 W, with corre-
lated color temperatures of 2900–6000 K, and in a variety of shapes.
The construction of the metal halide lamp is very similar to that
of the mercury vapor lamp. The major difference between the two
is the gas which fills the quartz arc tube. Where the mercury vapor
lamp contains a mixture of argon gases, with mercury for the arc,
metal halide lamps contain argon, mercury, and several different
iodide compounds. It is the iodides which produce light of a
superior spectral distribution, and give the metal halide light a high
CRI. Metal halide lamps are available with a variety of phosphor
coatings for the UV inhibiting outer tube to provide a desired corre-
lated color temperature. A second type of metal halide lamp, the
pulse start lamp, uses the same iodides and coatings, but instead of
using a filament coil, the arc is started using a high-energy pulse
The design tools 35

generated by an igniter, similar to a high pressure sodium lamp. In
addition to using an igniter circuit, the pulse start lamp differs from
the standard metal halide in several other ways:
1. an improved arc tube seal allows the lamp to run hotter with
higher fill gas pressure;
2. faster warm-up time (2–3 minutes);
3. faster hot re-strike time (3–4 minutes);
4. higher lumen output, and better performance (35% better than
universal burn metal halide);
5. longer life than the standard universal burn metal halide lamp.
In operation, the arc in the metal halide lamp is started by either
a combination of heated electrode/high starting voltages from the
ballast (standard) or by a high voltage pulse from the igniter
(pulsed start) to ionize the mercury in the arc tube. Once the arc
starts, the iodides gradually enter the arc stream, and the output
of the lamp shifts from the blue–green of mercury vapor to white.
Since the arc tends to curve upward when the lamp is horizontal,
some lamps are designed with a special curved arc tube to burn
horizontally. Others will burn in either a vertical or horizontal
(universal) position. The pulse start lamps are designed to burn in
the vertical position. In addition, the pulse start lamp requires a
pulse rated socket. As with the mercury vapor lamp, the ballast
required for metal halide operation must be closely matched to the
lamp.
The first letter in a metal halide lamp designator is ‘M’. The
second letter is a manufacturer’s letter to denote special features of
the lamp. The number following that designator is the wattage of
the lamp. A forward slash usually follows the wattage, and follow-
ing the slash is abbreviated data concerning the required burning
position, or the base type of the lamp. A M175/U lamp then, is a
175 W metal halide lamp which will burn in universal (either
horizontal or vertical) position.
Metal halide lamps offer many benefits, including:
1. highest efficacy of any ‘white’ light producing lamp;
2. long life (10 000–20 000 hours);
3. available in a variety of bases and shapes;
4. available in sizes from 50 to 2000 W;
5. available in a broad range of correlated color temperatures
(2900–6000 K);
6. high CRI (60–90);
7. insensitive to ambient temperature.
36 The Lit Interior

There are also a few drawbacks associated with metal halide lamps,
including:
1. requires warm-up time of 2–3 minutes;
2. must be used in a shielded fixture. Outer envelope breakage can
allow emission of high levels of UV light;
3. long restrike time after power outage (5–7 minutes – standard,
2–3 minutes – pulse start);
4. relatively expensive lamp.
Metal halide is a first choice for a wide variety of applications
requiring various mounting heights, including:
1. industrial facilities with high ceilings;
2. sports facilities;
3. warehouses needing high CRI;
4. retail facilities;
5. downlighting, uplighting, and accent lighting in commercial
facilities;
6. ambient lighting in facilities with high ceilings;
7. outdoor building lighting.
There is a metal halide option available for almost every type of
indoor luminaire. In sensitive areas, luminaires can be equipped
with a second, incandescent quartz lamp, to provide illumination
during the cool-down period in the event of a power dip. This is
called ‘quartz restrike’.
High pressure sodium lamps
High pressure sodium has the highest efficacy of any member of
the true HID family, and equals or exceeds the efficacy of fluores-
cent in all wattages. The drawback of the high pressure sodium
lamp is a low CRI, since almost 100% of the output light is in
the yellow–orange region of the spectrum. Construction of the
high pressure sodium lamp is similar to that of the other HID
lamps, with some notable exceptions. The arc tube is made of
ceramic material, rather than quartz, to withstand the corrosive
effects of sodium and the extremely high temperatures required
for operation. The arc tube is filled with sodium, and a small
amount of mercury and xenon gas for arc starting. No starting
electrodes are used in the standard sodium vapor lamp, so the
ballast includes an electronic igniter circuit that works in conjunc-
tion with the transformer to provide the high voltage to start the
lamp.
A hybrid sodium vapor lamp that includes the starting circuitry
inside the lamp has been developed to replace mercury vapor lamps
The design tools 37

in street lighting luminaires. This lamp will start on a standard
mercury vapor lamp ballast.
In operation, the lamp goes through a warm-up period of 3–4
minutes before reaching full brightness. During warm-up, the lamp
undergoes several color changes as the various elements ionize. As
the pressure in the arc tube increases, the lamp comes to full bright-
ness. A power outage or voltage dip will require only approximately
1 minute for restrike.
In operation in an open luminaire, the sodium vapor lamp
produces a ‘narrow spotlight’ light distribution pattern which
focuses most of the light in a small area. A diffusion coating on the
outer envelope is available for most sodium vapor lamps to spread
the distribution pattern. This is the ‘coated’ version of the lamp.
Unfortunately, this coating does not improve the CRI, which is only
about 21 for most lamps, unless phosphor coatings are used.
Phosphor coatings are available for the outer envelope of lamps
up to 400 W to improve the CRI to about 65, and for lamps up
to 100 W to produce a CRI as high as 85.
Manufacturers have chosen to call their high pressure sodium
vapor lamps by another name, ending in ‘lux’. Philips, for example,
calls theirs Ceramalux, while Osram–Sylvania calls theirs Lumalux.
The manufacturer descriptor for Osram–Sylvania, then, would start
with ‘LU’, for Lumalux. Following that is a number indicating
wattage, and after that, a forward slash. If a ‘D’ follows the slash,
this indicates a diffusion coating. If not, the following letters
indicate base type. For example, LU50/D/MED denotes a 50 W
high pressure sodium, coated, medium base lamp.
Benefits of high pressure sodium lighting are:
1. high efficacy;
2. available in sizes up to 1000 W;
3. no dangerous mercury arc in the event of outer envelope break-
age;
4. normal restrike in 1 minute or less – instant restrike available;
5. insensitive to ambient temperature;
6. long life (24 000+ hours).
The main drawbacks of high pressure sodium lighting are:
1. low CRI (21 without phosphor coating);
2. relatively expensive lamp and ballast;
3. extremely high operating temperatures – must be used in fixtures
which are ANSI designated for high pressure sodium use.
High pressure sodium lamps are widely used where CRI is not of great
importance, but where high lumen output is. These areas include:
38 The Lit Interior

1. parking lots;
2. warehouses;
3. loading docks;
4. streets and highways;
5. building floodlighting.
Low pressure sodium lamps
Although not a true high intensity source, the low pressure sodium
lamp is a discharge source, and is included here for completeness.
Low pressure sodium is a monochromatic source, having almost
100% of its light output in two narrow bands at 589 and 589.6
nanometers in wavelength, which is in the yellow portion of the
spectrum near the peak of the eye sensitivity curve. This gives low
pressure sodium the lowest CRI, and the highest efficacy in the
industry.
The low pressure sodium lamp is constructed much the same as
the high pressure sodium lamp, except that the ceramic arc tube is
bent into a ‘U’ shape, and dimpled to assure proper flow of the
vaporized sodium.
In operation, the lamp is started on neon–argon gas, and after a
warm-up period of 7–9 minutes the sodium vapor conducts, and
the lamp delivers full output. If a power outage occurs, the lamp
will re-strike in less than 1 minute.
The strong points of low pressure sodium are:
1. very high efficacy (as high as 200 lumens per watt);
2. low re-strike time
The drawbacks of low pressure sodium are:
1. monochromatic light output (very low CRI);
2. long warmup time;
3. relatively expensive.
Due to its low CRI, low pressure sodium has no interior applica-
tions. Its uses are primarily in large, outdoor applications where CRI
is of no consequence, such as railroad yards and parking lots. Table
2.2 is a performance comparison of the four types of HID lamps.
The design tools 39
Table 2.2. High intensity discharge (HID) performance comparison chart.
Light source Warm-up time Restrike time Efficacy (lumens/watt) Color rendering
Mercury vapor 5–7 min 3–6 min 30–55 Poor
Metal halide 2–5 min 10–20 min 60–95 Good, CRI 60–90
Pulse start metal halide 2–3 min 3–4 min 60–95 Good, CRI 60–90
High pressure sodium 3–4 min 1–2 min 60–125 Moderate
Low pressure sodium 7–10 min 3–12 s 80–180 Bad

Ballasts
Although not specifically a light source, ballasts are an integral part
of the fluorescent and HID lighting systems. The ballasts used with
these lamps serve two functions: (1) they start the arc in the tube
and (2) they regulate the current flow in the arc tube.
Lamps and ballasts must be properly matched in order to achieve
optimum (or any) operation. Let’s take a look at some of the differ-
ent ballasts.
Fluorescent ballasts
In general, there are three types of ballasts used with fluorescent
lamps. These are: magnetic, hybrid, and electronic.
Magnetic fluorescent ballasts
The magnetic ballast is the oldest of the three types, and has been in
service as long as fluorescent lamps have. The magnetic ballast is
basically a transformer consisting of a laminated steel core wrapped
with insulated copper or aluminum windings, and housed in a steel
case which is filled with a heat dissipating ‘potting’ compound. In
operation, the magnetic ballast supplies either line voltage to the
electrode coil to start a rapid start lamp, or high voltage across the
electrodes to start an instant start lamp. The windings of the trans-
former serve as a choke coil to limit current flow in the arc while the
lamp is operating. Magnetic ballasts lower the power factor of an
electrical system, and capacitors are often built into magnetic ballasts
to counteract this. Magnetic ballasts containing capacitors are called
high power factor ballasts. A magnetic ballast can control a maximum
of two lamps. There is a heating, or ‘ballast’ loss associated with the
use of magnetic ballasts. Ballast losses from magnetic ballasts can
account for up to 25% of total luminaire energy consumption.
Hybrid fluorescent ballasts
Hybrid ballasts are used only for rapid start lamps. A magnetic ballast
applies power to the starting coil during lamp start, and that power
continues to be applied while the lamp operates. The hybrid ballast is
identical in construction to the magnetic ballast, except that it contains
electronic circuitry to remove the coil power during lamp operation.
This reduces energy consumption by about three watts per lamp.
Electronic fluorescent ballasts
Electronic ballasts start and control current flow through fluorescent
lamps through the use of electronic circuitry, rather than transformer
40 The Lit Interior

windings. Electronic ballasts are similar to the power supplies found
in computers and other electronic devices: the incoming AC power
is rectified, regulated, and re-introduced into the system with differ-
ent characteristics. The electronic ballast operates the lamp at a much
higher frequency (20 000 Hz or greater) than the 60 Hz magnetic
ballasts, and thus eliminates lamp flicker and a host of other lamp
inefficiencies. Since there is no heavy steel core or windings involved
in the electronic ballast, it can be made smaller and lighter than the
magnetic ballast, and in operation, there is no ballast loss. One
electronic ballast can control up to four lamps.
The electronic circuitry used in the ballasts tends to distort the
waveform of the incoming power by injecting harmonics into the
system, notably the third harmonic. To counteract this, larger
power conditioning components are used in what are called low
THD (total harmonic distortion) ballasts. A word of caution here
– if the THD is too low (THD < 10%), the ballast inrush current
goes up dramatically, and there could be switching problems with
the luminaires. A ballast with a maximum THD of 15% is appro-
priate for most systems.
The high frequency of the electronic ballast also generates electro-
magnetic interference (EMI) which affects some sensitive electronic
equipment such as library book detectors, power line carrier control
systems, central time clock systems, and medical equipment. Hybrid
ballasts should be considered for use in areas where such equip-
ment is present. Otherwise, electronic ballasts should be the first
choice for all fluorescent applications.
High intensity discharge (HID) ballasts
High intensity discharge (HID) ballasts perform the same functions
that fluorescent ballasts do: they start the arc, and they regulate the
arc current once the arc is started. High intensity discharge ballasts
are magnetic, and each is designed to operate a particular lamp. In
general, there are four types of HID ballast: reactor, high reactance
autotransformer, constant wattage, and constant wattage autotrans-
former. Let’s look at some of the features of each type.
Reactor ballast
The reactor ballast is essentially just a choke coil in series with the
lamp which limits current through the lamp. The reactor ballast is
used with lamps which require only line voltage to start the arc,
such as mercury vapor lamps. The pros are that the reactor ballast
has low inrush current, and low cost; the cons are that the ballast
is very sensitive to line voltage, and lamp output can vary up to
The design tools 41

12% with a 5% variance in voltage. With about a 10% dip in line
voltage, the lamp arc will extinguish. Reactor ballasts have a low
power factor, and are often used in conjunction with capacitors to
remedy this. The manufacturer’s symbol for a reactor ballast is ‘R’.
High reactance autotransformer ballast
This ballast is an autotransformer, which means that it has two
windings connected electrically, and coupled magnetically. The high
reactance autotransformer ballast can boost line voltage to any
starting voltage required by the lamp. The windings also serve to
limit current through the lamp, as in the reactor ballast. Like the
reactor ballast, the high reactance autotransformer ballast is suscep-
tible to low line voltage, and has poor power factor. Since there is
an additional winding, this ballast is more expensive that the
reactor ballast. This ballast has a manufacturer’s symbol of ‘HX’.
Constant wattage ballast
The constant wattage ballast is a true two-winding transformer,
having only magnetic coupling between the coils. This configura-
tion is inherently insensitive to drops in the input voltage, and the
ballast can sustain up to a 50% dip in line voltage before the lamp
arc extinguishes. The constant wattage ballast contains a capacitor
for high power factor, and the starting current does not exceed the
lamp operating current. Unfortunately, these ballasts are expensive,
often costing three times as much as a reactor ballast. The ballast
has a manufacturer’s symbol of ‘CW’.
Constant wattage autotransformer ballast
This ballast is an autotransformer, with the two windings electrically
connected and magnetically coupled to provide excellent voltage
regulation. This ballast can withstand a 30% dip in line voltage
before the lamp arc is extinguished. With its built-in capacitor for
high power factor, and its low inrush current, this ballast offers the
best compromise between cost and performance. Its symbol is ‘CWA’.
For the more visual oriented among you, Figure 2.8 is a
schematic comparison of the four types.
You should always specify constant wattage (CW or CWA)
ballasts for HID luminaires which are fed from panels that also
contain heavy motor loads. Industrial motors have an inrush
current of 5–10 times their running current, and the inrush can last
for several seconds. If the motor is large enough, this can cause a
momentary voltage dip of 15–20% at the panel. Reactor ballasts
connected to the panel will drop their lamps out, and the place will
go dark – and remain so for the cool-down period of the lamp. It
42 The Lit Interior

is especially embarrassing to the lighting designer when the lights
go out every time the compressor comes on.
Luminaires
A luminaire is a complete system for providing the kind of light we
want, where we want it. The luminaire consists of the lamp, the
lamp socket, the ballast, if required, the reflector, diffuser, shield-
ing, and the housing for all those things. A luminaire needs only a
mounting spot and a source of electricity to produce light.
To be an efficient producer of light, a luminaire must provide
balanced, glare-free illumination. Luminaires accomplish this
through the use of reflectors, which shape the light output, and
shielding and diffusion devices that reduce glare and distribute the
light evenly. Let’s take a look at these components.
Reflectors
Reflectors are bent painted metal panels in an inexpensive fluores-
cent luminaire, or precisely cut or vacuum-formed mirror finish
optical systems in an expensive architectural downlight, or anything
in between. Reflectors serve a twofold purpose: they shape the light
The design tools 43
Figure 2.8. Ballast schematics (source: Advance Transformer).

pattern of the luminaire, and they improve the efficiency of the
luminaire (defined as the amount of light delivered by the luminaire,
divided by the light produced by the lamps) by directing the usable
light out of the luminaire onto the work surface. Glossy or mirrored
reflectors produce direct light, while matte finish reflectors produce
scattered, or diffuse light.
Factors affecting the performance of a reflector are the reflectiv-
ity of the reflector material and the optical geometry of the reflec-
tor. Reflectivities range from about 60% for standard white paint
to 95% for polished aluminum. The geometry of the reflector largely
determines the shape of the light pattern emitted by the luminaire.
Over the years, luminaire manufacturers have experimented with
various shapes of reflectors to improve performance. One shape in
particular which has proven effective in ceiling-mounted fluorescent
fixtures is the parabola: a reflective trough in the shape of a
parabola is installed lengthwise in the luminaire, and the fluores-
cent tube is mounted at the apogee of the parabola. Figure 2.9 is
a ray trace of the parabolic reflector.
Another interesting geometric shape used for lighting purposes is
the ellipse. When used in a recessed downlight, an elliptical reflec-
tor can be designed such that its focal point is exactly at ceiling
level. The focal point in an elliptical reflector is that point at which
all reflected light rays converge. Past that point, they diverge again.
This allows all the light produced by the lamp to be passed through
a very small opening in the ceiling. This is called a ‘pin-hole’
luminaire, and its ray trace is shown in Figure 2.10.
Shielding and diffusion devices
Shielding devices are used to reduce the glare produced by a
luminaire; diffusion devices are used to diffuse the produced light,
and to conceal the bare lamps of the luminaire.
44 The Lit Interior
Figure 2.9. Parabolic reflector ray trace.

Baffles
An example of a shielding device is the baffles used in conjunction
with the parabolic reflectors in a recessed parabolic luminaire.
Figure 2.11 illustrates this luminaire.
It is seen that the baffles running along and perpendicular to the
sides of the parabolic trough form multiple ‘cells’ along the length
of the luminaire. These cells provide sharp cut-off glare shielding
when the luminaire is viewed at an angle. The smaller the cells are,
the better the control. However, since the baffles are made of
opaque material, small cells tend to mask much of the light
produced by the luminaire, and thereby reduce its efficiency.
Diffusers
Diffusers used with fluorescent fixtures also influence the distribu-
tion pattern of the luminaire. The most common diffuser employed
The design tools 45
Figure 2.10. Elliptical reflector ray trace.
Figure 2.11. Baffles in a parabolic luminaire (source: Lithonia Lighting).

in fluorescent fixtures used for general area lighting is a flat plastic
sheet embossed with some sort of diffusion pattern. The two most
common plastics used for this purpose are polycarbonate and
acrylic. Polycarbonate is exceptionally strong, but unless specially
treated to resist the UV emissions from the lamp, will turn yellow
after a period of time. Acrylic, though not as strong, is impervious
to UV. Acrylic diffusers are made as thin as 0.10 in. (0.25 cm) thick
for a 2 ft ⫻ 4 ft (0.6 m ⫻ 1.2 m) unit, but since this material is not
especially strong, sheets this thin will tend to sag in the luminaire.
It is always best to specify UV-treated polycarbonate, or acrylic
diffusers no less than 0.125 in. (0.318 cm) thick. There is a variety
of diffuser styles available in either material which can produce a
desired distribution pattern.
Luminaire housings
Housings for luminaires can be metallic, such as sheet steel or
aluminum for general purpose, or plastic for corrosive or high
abuse areas. Luminaires that fit into standard 2 ft ⫻ 4 ft grid (0.6 m
⫻ 1.2 m) ceilings are available with air-handling housings, which
can serve as return or supply registers for the building HVAC
(heating, ventilating, and air conditioning system). A benefit of this
type of housing is that luminaire heat is removed before entering
the space.
Luminaire classifications
Luminaires used for area lighting have been classified by the Illumi-
nating Engineering Society (IES) according to their distribution
pattern and by the downward and upward component of the light
generated. In general, there are five categories of luminaire: direct,
semi-direct, general diffuse, semi indirect, and indirect. The
distinguishing patterns of four of these types is shown in Figure
2.12a–d.
The general diffuse lighting pattern is one that contains equal
components in all directions.
Direct illumination
Direct illumination, as shown in Figure 2.12a, is the most efficient
use of the luminaire to provide lumens to the work area. It also
produces the greatest amount of glare, unless shielded. Direct illumi-
nation is best used where you desire a high ambient lighting level,
such as kitchens, day care centers, and general work spaces. Direct
46 The Lit Interior

illumination is also used for task lighting, where a high lighting level
in a limited area is desired. When used with parabolic reflectors and
baffles, or cutoff shielding, direct illumination is acceptable for use
in areas where glare is undesirable, such as offices containing video
The design tools 47
Figure 2.12. (a) Direct illumination, (b) semi-direct illumination, (c) semi-indirect illumination,
(d) indirect illumination (source: F.H. Jones).
(a) (b)
(c) (d)

data terminals. Direct luminaires may be recessed into the ceiling,
surface-mounted on it, or suspended below it.
Semi-direct illumination
Semi-direct luminaires have an upward component, as shown in
Figure 2.12b, so they must be either surface-mounted or suspended.
They are used for the same purpose as direct luminaires, except that
when suspended, the upward component lights the ceiling, and
eliminates the ‘cave effect’ produced by the suspended direct
luminaire.
Semi-indirect and indirect illumination
The semi-indirect and indirect luminaires must be suspended to
utilize the upward reflected component of light. These luminaires
differ only in the percentages of uplight and downlight that they
produce. Indirect luminaires produce almost 100% uplight, which
provides a diffuse, glare-free illumination particularly well suited
for use in a room with heavy computer terminal usage. Most
manufacturers offer an indirect luminaire which produces about
10% direct illumination to eliminate the dark area created by the
luminaire housing.
Wall-mounted luminaires are classified in the same manner as
ceiling-mounted ones, and have basically the same illumination
patterns. One type of wall-mounted luminaire that receives consid-
erable use in modern buildings is the cove light, which is usually
mounted near the ceiling, and is used in an indirect pattern to
illuminate the ceiling. Figure 2.13 shows a typical cove lighting
installation.
48 The Lit Interior
Figure 2.13. Cove lighting (source: author).

Luminaire photometric data
Manufacturer’s published information for their luminaires includes a
graphic representation, in two axes, of the distribution pattern
produced by each luminaire. This representation is called a candle-
power distribution curve for the luminaire. It is also called a ‘batwing’
curve in the industry, because of the distinctive shape of some curves.
Figure 2.14a and b shows candlepower distribution curves for a
recessed HID direct pattern downlight luminaire, and a recessed
fluorescent direct pattern downlight luminaire, respectively.
These curves were generated in test laboratories by taking candle-
power measurements around a test luminaire and plotting them on
polar coordinates. In applications where all the light from the
luminaire is projected in one direction, such as the direct distribu-
tion of the luminaires in Figure 2.13, only half of the polar graph
is shown. We can use this published data to give us some idea of
the light pattern which a particular luminaire will provide. Distri-
bution curves are a valuable tool for quickly evaluating luminaire
suitability, especially for task lighting applications.
Lighting calculations
The distance from the center point of the candlepower distribution
curve to any point on the curve gives the lumens of the luminaire
The design tools 49
Figure 2.14. Candlepower Data for (a) HID and (b) fluorescent downlights (source: Lithonia
Lighting).
(a))
(b))

in that direction. For asymmetric luminaires, such as a 2 ft ⫻ 4 ft
(0.6 m ⫻ 1.2 m) fluorescent luminaire, data is given for each of the
two axes of the fixture: along the length of the luminaire, or paral-
lel to it; and across the luminaire, or perpendicular to it.
Now, if you remember the inverse square law and the cosine law
of incidence from Chapter 1, and you know the distance and direc-
tion of your chosen luminaire from a surface that you want to
examine, you can calculate the footcandles on that surface. For
example, suppose you were interested in finding the footcandles
produced on a desk by the fluorescent luminaire in Figure 2.14b.
The center of the desk is 10 ft from the luminaire, and at an angle
of 30°. You can look at the distribution curve and read the lumens
at 30°. Using the cosine law of incidence, I = L cos X/D2
, the illumi-
nation produced at the center of the desk by this one luminaire is:
Lumens ⫻ 0.866/100, for footcandles on the square foot at the
center of the desk.
Some manufacturers produce the lumen values at the various
angles in tabular form, and the total lumens in an angular zone are
shown. The angles listed are measured from the vertical, or normal
to the luminaire. Figure 2.15 is one such set of distribution data.
As seen in Figure 2.15, a lot of other luminaire information is
included in the manufacturer’s data, or ‘cut’ sheets. The coefficient
of utilization (CU) of the luminaire, as shown in the table, is a
ratio of the lumens which reach an assigned working plane to the
total lumens generated by the lamps in the luminaire. Many factors
contribute to the coefficient of utilization, including luminaire
efficiency and distribution pattern, room geometry and
reflectances, and luminaire mounting height. The coefficient of
utilization is useful for general area calculations, such as the
lumen, or zonal cavity calculation method, which yields an
approximation of the average lumens per square foot of the space
under examination.
Zonal cavity calculations
Zonal cavity calculations are a quick manual method of estimating
average footcandles, or the number of luminaires required to
produce a desired average footcandle level within a defined space.
To get some idea of how a zonal cavity calculation works, let’s take
a hypothetical office space which is 20 ft ⫻ 20 ft, with a 9 ft ceiling.
The interior designer has selected a white ceiling tile with a
reflectance of about 0.8, a light gray semi-gloss wall paint with a
reflectance of about 0.7, and a darker gray carpet with a reflectance
of 0.2. The work plane is the desktop, at 2.5 ft above the floor.
50 The Lit Interior

The luminaire that we will use for the office is the 2GT432A12
fluorescent luminaire of Figure 2.15. The luminaire will be mounted
in the ceiling grid.
The design tools 51
Figure 2.15. Candlepower data, Lithonia 2GT432 (source: Lithonia Lighting).

The zonal cavity method entails dividing the space into three
cavities: the ceiling cavity, which is that space above the luminaire;
the room cavity, which is the space between the luminaire and the
work plane; and the floor cavity, which is the space below the work
plane. We have no ceiling cavity in this example, since the
luminaires are mounted directly in the ceiling. The room cavity
extends from the desk top to the ceiling, a distance of 9 ft - 2.5 ft
= 6.5 ft. The floor cavity is 2.5 ft deep. We are primarily interested
in illuminating the room cavity, since that’s where all the activity
will take place. Let’s hypothesize a little further and say that we
have defined the lighting criteria for this office space to be 70
footcandles (70 fc) at the desktop. (You’ll learn more about defin-
ing lighting criteria in the next chapter.) What we need to find out
by our zonal cavity calculation is how many luminaires will be
required in this space to provide that 70 fc.
The zonal cavity method allows us to calculate a cavity ratio for
the cavity under examination, which in our case is the room cavity.
By calculating the room cavity ratio (RCR) for our space, we will
be able to select the proper coefficient of utilization using the
manufacturer’s tables. The formula for calculating a cavity ratio is:
CR = 5H ⫻ (room length + room width)
(room length ⫻ room width)
where H is cavity height.
In our case, the RCR of the office is:
5(6.5 ft) ⫻ (20 ft + 20 ft)
= 3.5
(20 ft ⫻ 20 ft)
Now, if we go back to the coefficient of utilization table in Figure
2.15, we see that, with a RCR of 3.5, the CU can be interpolated
as 0.645, using the reflectances mentioned earlier.
The zonal cavity method calculates average illumination by deter-
mining the total number of usable lumens produced by the lighting
system, and dividing that number by the number of square feet in
the space. This yields an average lumen/sq. ft (sq. m), or footcan-
dle value at the work surface. Conversely, if the desired footcan-
dles is given, the number of luminaires required to produce those
footcandles may be calculated.
The usable lumens produced by a luminaire in a space depends
upon a number of things: first is the maximum number of lumens
that the luminaire is capable of producing. This depends on how
many lamps the luminaire has, how many lumens each lamp will
52 The Lit Interior

produce, and the ballast factor (BF) of the ballast. Manufacturer’s
data for the luminaire indicates the number of lamps in the
luminaire, and often lists lamp lumens, as well. If not, lumens can
be found in lamp catalogs.
Easy for me to say, right? OK – you won’t find a lamp catalog
in the public library, maybe not even in a college library, but this
is the twenty-first century. We’ve got the Internet. Most lamp
manufacturers have a Web site, and we’ll find out how to access
them a little later.
Ballast factor is a decimal number, usually less than 1, which
compares the performance of the ballast in the luminaire with that
of the standard laboratory ballast used to determine the lamp lumen
output listed in the lamp catalogs. Ballast factor can be specified,
or obtained from the luminaire manufacturer. A BF of less than 1
means that the lamps will produce less than the listed lumen output,
since actual output is obtained by multiplying listed output times
the BF. Ballasts are available with BF of greater than 1, which
means that the lamps will produce more than listed output. In
general, the lower the BF, the less the lumen output, and the less
energy the luminaire will use. If the BF cannot be obtained from
the manufacturer, use 0.80.
Using all of the above factors, we can design for an approximate
initial lighting level in the space. If we want to design for a
maintained lighting level, we must consider some things that will
happen after the system is installed. The first of these is lamp lumen
depreciation (LLD). As a lamp ages, its light output becomes less.
The major lamp manufacturers have done sufficient testing to be
able to predict fairly accurately how their lamps will perform over
time. The normal design point is at 70% of the lamp’s lifetime, and
the manufacturers usually list a mean, or design lumen value for
their lamps at that point. A typical 32 W T8 fluorescent lamp which
operates 12 hours per start has an LLD of 0.86. Another factor
which affects fixture performance over time, but which is harder to
quantify, is lumen dirt depreciation (LDD) of the fixtures and the
surfaces in the space. No matter how many charts and graphs you
may see on this subject, LDD is dependent on the use of the space,
and the quality of the maintenance of that space. In our office
space, if the maintenance staff changes the HVAC filters regularly,
and if they clean the luminaire each time they change a lamp, we
could expect an LDD of about 0.85.
Now that we’ve thought through how our system will perform
in the office space, let’s use the zonal cavity method to calculate
the number of luminaires of the type shown in Figure 2.15 that will
be required to give us an average of 70 fc throughout the space.
The design tools 53

We have said that the average FC level =
Total usable lamp output (lumens)
Area of the space (sq. ft)
And the usable lamp output is:
(No. of Luminaires) ⫻ (Lamps/Luminaire) ⫻ (Lumens/Lamp)
⫻ BF ⫻ CU ⫻ LLD ⫻ LDD
So, by doing a little mathematical gymnastics, we can say that
Desired Average FC Level ⫻ Area
(No. of Luminaires) =
(Lamps/Luminaire) ⫻ (Lumens/Lamp)
⫻ BF ⫻ CU ⫻ LLD ⫻ LDD
All we have to do now is plug in the values, and turn the crank:
Desired footcandles = 70
Area = 20 ft ⫻ 20 ft = 400 sq ft
Lamps/Luminaire = 4
Lumens/Lamp = 2850 lumens – from lamp catalog data (we
will see later how to get this).
BF = 0.80 (assumed BF for generic electronic ballast)
CU = 0.68
LDD = 0.80
LLD = 0.86
Plugging all this in, we get:
70 ⫻ 400
No. of luminaires =
4 ⫻ 2850 ⫻ 0.8 ⫻ 0.68
= 6.56
⫻ 0.80 ⫻ 0.86
Since we cannot buy 0.56 of a luminaire, we’ll use six luminaires
and get a little less than 70 fc.
Now that we’ve done all this high level calculating, with decimal
points and everything, we can be sure that, if we put six luminaires
in the ceiling of that space, we’ll have 70 fc at 30 in. above the
floor everywhere in the room, right? Wrong! If you took a light
meter into the space after the six luminaires were installed, you
would be hard pressed to find a 70 fc reading anywhere in the
room. That would only happen if the output from those six
luminaires were spread evenly throughout the ceiling of the room,
because what we have calculated is average illumination. As it is,
we have 48 square feet of light source (six individual 2 ft ⫻ 4 ft
luminaires) to place in 400 square feet of ceiling. If we put them
54 The Lit Interior

all in one corner of the room, we would have considerably more
than 70 fc there, but much less everywhere else. We would still have
an average of 70 fc in the room.
What we try to do in general area illumination situations like this
is to distribute the six luminaires such that their spacing from each
other, and from the walls is approximately equal, to get the best
distribution of light possible. Since the luminaires are asymmetric,
we measure our spacing from the center point of the luminaire.
The manufacturer’s information for our luminaire, shown in
Figure 2.15, indicates the spacing criterion, S/MH, or maximum
distance between luminaires, is 1.2 ⫻ mounting height in the long
direction. Note that this is the mounting height above the working
plane, not the floor. In our case, this is 1.2 ⫻ 6.5 ft, or approxi-
mately 8 ft. It is always best to maintain the published spacing crite-
rion in your designs, in order to achieve relatively even illumination
throughout the space.
Now let’s lay out those six luminaires in the space, and calculate
the illumination at 2.5 ft from the floor on a 1 ft ⫻ 1 ft grid every-
where in the space, using the cosine law of incidence. Bear in mind,
that there are six luminaires, so we have to calculate the contribu-
tion of each luminaire at each point on the grid, and then add them
up to get the total illumination at that point. This is a nice little
exercise to do on a two-week holiday, or we can call in the computer.
Computerized calculations
There are a number of commercially available point-by-point light-
ing calculation programs, and many of them are based around the
ray tracing calculation engine of the LUMEN MICRO program, the
original calculation program developed by Lighting Technologies,
Inc. Others are based around a luminous rate of transfer calcula-
tion engine, such as the one that we will use in our calculations.
For our computer calculations throughout this book, we will use
VISUAL BASIC, a program developed by Lithonia Lighting, a large
lighting company located in Conyers, GA, USA. VISUAL BASIC is
available as a free download on Lithonia’s Web site, www.litho-
nia.com. We should now get on the Internet, and go to this site.
From the opening welcome screen, we select the VISUAL
download section, and in this section, we see the software options.
Several offerings appear here, the ‘Visual 2.0 SP1’ option, the
‘Photometrics’ option, and the ‘Basic edition users guide’ option.
The Visual 2.0 SP1 package contains the calculation package, and
we should download the package that is compatible with our
computer’s operating system. Once this download is complete, we
The design tools 55

need to download the users guide for reference. This will give us a
calculation program, and instructions for using it. The next thing
we need to do is to download some photometrics for luminaires,
which we will use in our exercises. We go back to the ‘Photomet-
rics option’, and go into the Lithonia library of IES files. These files
provide the performance data for the luminaires, which we will be
using in our examples. This data is in digital IES format, and it is
the same data that is published in the manufacturer’s performance
charts, such as that shown in Figure 2.15.
In the Lithonia library, we see that data is available for many
different types of lighting. You can download the whole library if
you have a lot of free hard drive space, and you will be able to run
calculations using any luminaire made by the Lithonia group. For
our immediate purposes, though, we only need to download the
fluorescent lighting group, which contains architectural downlights,
lensed troffers, parabolics, etc.
Once you complete these downloads, you need to install the
VISUAL BASIC program by clicking on the self-extracting ‘.exe’ file
which was downloaded. Now we are ready to run a computer
calculation. (Note: Web sites are changed from time to time, so the
procedure above may not exactly fit the Web site as it exists when
you visit it. All of the information will be there, though, and a little
navigating around the site should allow you to download the latest
versions of the files.)
The VISUAL program was developed by the Lithonia Lighting
group as a design tool for lighting designers and specifiers. It is
intended for use on personal computers, utilizing catalog and
photometric data for all the luminaires manufactured by the Litho-
nia group, both interior and exterior. It will also use photometric
data from other manufacturers, provided that the data is in IES
format. The design program contains calculation engines and layout
modeling capabilities.
There is an advanced version of the VISUAL program, called
VISUAL PRO, which contains many more features than the
VISUAL BASIC program, including the ability to import digital
drawing files to allow lighting layout and calculations to be
performed using actual floor plans, or site plans. VISUAL PRO is
available for purchase from Lithonia Lighting.
For our example office space, we will use the internal layout
editor in our downloaded VISUAL BASIC program. Just fill in the
blanks in the layout screens to input the room geometry and
reflectances. For a ceiling type, we’ll use a 2 ft ⫻ 2 ft grid.
The program allows the designer to select photometric data from
any of the luminaires in the Lithonia group to use for the calcula-
56 The Lit Interior

tions by entering an electronic ‘catalog’ and selecting the desired
luminaire. You do this by selecting the file icon next to the ‘photo-
metric file’ input field. Then select ‘fluorescent’, ‘lensed troffers’,
and you’ll see all the lensed troffers that Lithonia makes. Select a
2GT432 troffer as seen in Figure 2.15, and the program will load
the same photometric data that is represented in tabular form in
Figure 2.15, except that it is in IES standard format electronic form.
We select the standard LLF for a lensed troffer, and put in the
desired 70 fc. Our layout now shows six luminaires, which is about
what we would expect, since our zonal cavity calculation showed
that we need 6.3 luminaires. We can now run the calculator and
find out the point-by-point footcandle values for each point on our
1 ft ⫻ 1 ft grid in a flash. How clever we are. Wait a minute. . .
the average footcandle reading for this arrangement is higher than
the zonal cavity calculation! How could this be? Well, this is
because the particular luminaire that we selected has a little better
performance than the generic one we conjured up for the zonal
cavity calculations. This is another benefit of computer calculations.
You can use the real IES performance data for the real luminaire
instead of interpolating from a generic photometric chart. The
results of our computer run are shown in Figure 2.16.
The design tools 57
Figure 2.16. Office VISUAL results.

Clearly, the computer is the way to go if you are looking for
accurate illumination values for a space, especially if you’re using
more than one type of luminaire, or if there are obstacles in the space.
Still, the zonal cavity calculation method can provide a quick average
illumination estimate if you don’t have your computer handy.
Controls
Controls are what you use to make your lighting system behave as
you want it to. Controls are discussed in depth in Chapter 4, but
it will be useful to know the basic concept behind the devices, so
you can do the exercises in the next chapter. The most commonly
used forms of lighting control are:
• Switches – on–off manual devices that control the power to the
system.
• Dimmers – devices that reduce the light output of the luminaires
in the system; incandescent lamps are dimmed directly, fluores-
cent lamps require a special dimming ballast.
• Photocells – devices that turn the luminaires on when no light
is present, and off when light is present.
• Timers – devices that turn the lights on and off at preset times.
• Occupancy sensors – devices that turn the lights on when the
space is occupied, and off when it isn’t.
And that about covers it. A quick bagful of nifty devices that you
can use to make your lighting system function just as you want it
to. You’re only limited by budget and imagination.
Now let’s look at another kind of limits – those imposed by the
regulatory agencies that impact our design and the way that it is
built.
Standards, codes, and design guidelines
(Note: The following section lists only US Codes and Standards,
and is included to illustrate the application of standards in lighting
design. The reader should become familiar with the comparable
codes and standards which govern in his or her locale, and apply
them in a similar fashion)
Although not design tools per se, lighting standards, codes, and
design guidelines influence the selection of lamps and luminaires,
and can set the tone for the design. It is useful to the designer to
58 The Lit Interior

be familiar with the standards and codes with which the design
must comply. It is also useful to be aware of recognized design
guidelines, and to take advantage of the many hours spent by others
in developing them. Let’s look now at some of these standards and
guidelines that apply directly to interior lighting design.
NFPA-70:The National Electric Code
The National Electric Code (NEC) is the governing code for all the
electrical installations within the US. Virtually every county in every
state has adopted the NEC in whole, or in part, into their own
electrical code. You can be sure, as a designer, that the installation
of your design will come under the scrutiny of the building inspec-
tor – who is looking for violations of the NEC.
The NEC is a product of NFPA (The National Fire Protection
Association), and therefore the focus of the document is the preven-
tion of fires. Luminaires are heat-producing devices, so this is a
genuine concern. Article 410 of the NEC addresses both the instal-
lation and the manufacture of luminaires. It contains a lot of useful
information with which the designer should become familiar.
NFPA 101 – The Life Safety Code
The Life Safety Code is another NFPA product, so the focus is on
personnel safety in the event of a building fire. The code covers
several of the most common building types, and specifies the type
and amount of exit and emergency lighting required for each. Every
lighting design must meet these requirements, so every designer
needs to be familiar with them.
ASHRAE/IES Standard 90.1
Standard 90.1 is a US National energy standard developed jointly by
the American Society of Heating, Refrigeration, and Air condition-
ing Engineers (ASHRAE), and the Illuminating Engineering Society
of North America (IESNA). It mandates the maximum energy
consumption allowable for HVAC and lighting systems in new
construction. Meeting the Standard 90.1 requirements is mandatory
for all new US Government construction, and most states have
adopted it as well. It is only a matter of time before all building
departments adopt the Standard, so lighting designers should begin
complying with the standard now.
Standard 90.1 addresses lighting by establishing lighting power
budgets for various types of buildings and activities. The interior
The design tools 59

lighting power allowance may be determined for the building as a
whole, or on a space-to-space basis. Figure 2.17 lists the allowable
lighting power density for various types of buildings.
In calculating power usage either within a building or a space,
the total allowable luminaire wattage may be found by multiplying
the square footage of the space times the allowable power density.
When using the space-by-space calculation method, the total build-
ing installed lighting power is the sum of the power calculated for
all the spaces.
Certain types of lighting are exempt from the allowable power
calculations. Specifically, these are:
1. display lighting in museums, galleries, and monuments.
60 The Lit Interior
Table 2.3. Lighting power densities using the building area method
Building type Lighting power density (W/ft2
)
Automotive facility 1.5
Convention center 1.4
Court house 1.4
Dining: bar lounge/leisure 1.5
Dining: cafeteria/fast food 1.8
Dining: family 1.9
Dormitory 1.5
Exercise center 1.4
Gymnasium 1.7
Hospital/health care 1.6
Hotel 1.7
Library 1.5
Manufacturing facility 2.2
Motel 2.0
Motion picture theater 1.6
Multi-family 1.0
Museum 1.6
Office 1.3
Parking garage 0.3
Penitentiary 1.2
Performing arts theater 1.5
Police/fire station 1.3
Post office 1.6
Religious building 2.2
Retail 1.9
School/university 1.5
Sports arena 1.5
Town hall 1.4
Transportation 1.2
Warehouse 1.2
Workshop 1.7
(Reprinted by permission from ASHRAE Standard 90.1-1999. Copyright 1999, American Society of Heating,
Refrigerating and Air-Conditioning Engineers, Inc. Contact ASHRAE at 404-636-8400 or www.ashrae.org to purchase
the standard in its entirety)

Figure 2.17. Lighting power densities using the space-by-space method. (Reprinted by permission from ASHRAE Standard 90.1-1999.
Copyright 1999, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. Contact ASHRAE at 404-636-8400 or
www.ashrae.org to purchase the standard in its entirety)

2. lighting integral to equipment, such as medical and food service
equipment;
3. lighting for plant growth;
4. lighting in spaces specifically designed for use by the visually
impaired;
5. lighting in retail display windows, provided that the display
area is enclosed by ceiling height partitions;
6. lighting in interior spaces that have been specifically designated
as a registered interior historic landmark;
7. lighting that is an integral part of advertising, directional, or
exit signage;
8. lighting that is for sale or lighting educational demonstration
systems;
9. lighting for theatrical purposes, including performance, stage,
film and video production;
10. lighting for athletic playing areas with permanent facilities for
television broadcasting;
11. casino gaming areas.
Normally, you would only use the whole building method for
projects where the whole building is the space, such as a warehouse,
or retail facility. The space-by-space method allows tradeoffs
between the spaces, as long as the total building installed power
usage does not exceed the interior lighting power allowance for the
building type.
In some cases, Standard 90.1 allows an increase in the interior
power allowance when using the space-by-space method for calcu-
lating installed interior lighting power. These increases are:
1. 1 watt per square foot when decorative lighting, such as
chandeliers and sconces, are installed for highlighting purposes
in addition to the general lighting;
2. 0.35 watts per square foot when required to meet task require-
ments in video display terminal areas;
3. 1.6 watts per square foot for highlighting general merchandise,
and 3.9 watts per square foot for highlighting jewelry in retail
facilities.
Standard 90.1 also includes a clause which makes it mandatory that
every building larger than 5000 square feet contains an automatic
control device to shut off building lighting in all spaces. This device
can be controlled by either a timer, an occupancy sensor, or a
switch. In addition, each space must contain a control device for
the lighting within the space. The Standard also specifies additional
control requirements for specialized applications.
62 The Lit Interior

Control of the space lighting within the space is standard good
practice, and is currently in use throughout the industry. A central
control point for all building lighting will require some forethought
on the part of the designer.
A 100% adoption of Standard 90.1 by building codes agencies
will create some changes in current lighting design practices, and
the fledgling designer will do well to become familiar with this
Standard.
EPACT 92
EPACT 92, or the national Energy Policy Act of 1992, is a US
Government sponsored program to reduce the amount of lighting
energy consumed by the country. Where Standard 90.1 restricts the
energy consumption of the space, EPACT 92 restricts the energy
consumption of the lamps themselves. After November 1, 1995, the
manufacture or import of many of the then most popular lamp
types was forbidden by the Federal government. Failure to comply
with the Act could result in fines of up to $100.00 per lamp. At
that rate, getting caught with a truckload of illegal lamps would
put most people out of business. Needless to say, the lamp manufac-
turers have taken this Act to heart, and only those lamps with
acceptably high efficacy are available now.
This posed a lamp replacement dilemma for those who already
had thousands of fluorescent luminaires installed with ballasts
designed for the outlawed low efficacy fluorescent lamps. Lamp
manufacturers responded by producing lower wattage lamps that
would fit into the same luminaire, and operate on the same ballast.
But alas, there is no free lunch, even in lighting, and less watts
meant less light output. In installations that were already border-
line, this resulted in some dimly lit office space.
There is a great movement toward retrofitting existing luminaires
with high efficacy lamps and electronic ballasts in order to get
acceptable lighting levels out of existing luminaire installations.
We’ll discuss this in greater detail in Chapter 6 ‘The Second Time
Around’.
IES recommended footcandles
The IES has, since 1947, published a lighting handbook which
recommends ambient footcandle levels for most kinds of interior
spaces. Later versions of the handbook take into account light
quality as well as quantity, and different categories of illumination
have been developed. Such factors as age of occupants, contrast of
The design tools 63

64 The Lit Interior
Table 2.4. Determination of illuminance categories.* (lx = lux, fc = footcandle.)
Orientation and simple visual tasks. Visual performance is largely unimportant. These tasks are found in
public spaces where reading and visual inspection are only occasionally performed. Higher levels are
recommended for tasks where visual performance is occasionally important.
A Public spaces 30 lx (3 fc)
B Simple orientation for short visits 50 lx (5 fc)
C Working spaces where simple visual tasks are performed 100 lx (10 fc)
Common visual tasks. Visual performance is important. These tasks are found in commercial, industrial
and residential applications. Recommended illuminance levels differ because of the characteristics of the
visual task being illuminated. Higher levels are recommended for visual tasks with critical elements of
low contrast or small size.
D Performance of visual tasks of high contrast and large size 300 lx (30 fc)
E Performance of visual tasks of high contrast and small size, or visual tasks 500 lx (50 fc)
of low contrast and large size
F Performance of visual tasks of low contrast and small size 1000 lx (100 fc)
Special visual tasks. Visual performance is of critical importance. These tasks are very specialized,
including those with very small or very low contrast critical elements. Recommended illuminance levels
should be achieved with supplementary task lighting. Higher recommended levels are often achieved by
moving the light source closer to the task.
G Performance of visual tasks near threshold 3000–10 000 lx
(300–1000 fc)
*Expected accuracy in illuminance calculations are given in Chapter 9 of the IESNA Lighting Handbook,
Lighting Calculations. To account for both uncertainty in photometric measurements and uncertainty in
space reflections, measured illuminances should be within ±10% of the recommended value. It should
be noted, however, that the final illuminance may deviate from these recommended values due to
other lighting design criteria. (Source: IESNA Lighting Handbook, 9th edn.)
I. INTERIOR Very Important Important Somewhat important Blank = Not important or not applicable
LOCATIONS AND TASKS
Design
Issues
Appearance
of
Space
and
Luminaires
Color
Appearance
(and
Color
Contrast)
Daylighting
Integration
and
Control
Direct
Glare
Flicker
(and
Strobe)
Light
Distribution
on
Surfaces
Light
Distribution
on
Task
Plane
(Uniformity)
Luminances
of
Room
Surfaces
Modeling
of
Faces
or
Objects
Point(s)
of
Interest
Reflected
Glare
Shadows
Source/Task/Eye
Geometry
Sparkle/Desirable
Reflected
Highlights
Surface
Characteristics
System
Control
and
Flexibility
Special
Considerations
Notes
on
Special
Considerations
Illuminance
(Horizontal)
Category
or
Value
(lux)
(
a
)
Illuminance
(Vertical)
Category
or
Value
(lux)
(
a
)
E C
(14,15) D B
(14,15) E B
E B
C A
E A
C A
(1) C A
(1) E A
(1) E
Notes:
(1) Consider lighting for video cameras.
(13) Design issues, including illuminances, can be listed for room or space. Refer to specific task under Reading or Graphic Design and Materials, for example.
(14) Lighting should be flexible to accommodate changes in office furniture
(15) Accoustical aspects of luminaires need to be considered
Offices (13)
Filing (see Reading)
General and private offices (see Reading)
Open plan office
Intensive VDT use
Open plan office
Intermittent VDT use
Private office
Libraries (see Libraries)
Lobbies, lounges, and reception areas
Mail sorting
Copy rooms
Lobby
Customer service counter
Mail processing, general
Parking Faci ities (see Section III, Outdoor)
Post Ozzffices
Figure 2.18. IESNA Lighting Design Guide excerpt (source: IESNA Lighting Handbook, 9th edn).

tasks, use of video display terminals (VDTs) and degree of detail
are weighted into the recommendations for various activities within
those spaces. These recommendations are updated periodically to
take into account such factors as new technology and energy trends.
These recommendations are the result of a great number of hours
of work and research by IES members, and they are recognized indus-
try wide as a design standard. A good lighting designer is well advised
to take advantage of the work that has been done, and to use these
recommendations as a basis of design. Table 2.4 is an excerpt from
the IES lighting Handbook Reference and Application, Ninth
Edition, which explains the illumination categories of the IES Guide-
lines. Figure 2.18 shows the IES design guide listings for offices.
Well, OK, now you know enough to select a lamp to provide
the proper type and color of light for your design space, and you
can select a type of luminaire to put the light into the work area.
You can control the luminaires, and you know where to find the
proper illumination level for your space and activity. Then you can
calculate the number of luminaires required to give you that level.
So, armed with this knowledge, you are ready to venture forth into
the world of design techniques to try your wings. But first, as
always, let’s try a few of these fun-filled exercises to refresh our
memory.
Exercises
1. What are the two most important methods by which we can
produce light by using electricity?
2. How does incandescence produce light?
3. How does photoluminescence produce light?
4. What do spectral energy distribution curves tell us about a light
source?
5. What does the CRI number tell us about a light source?
6. Why is an incandescent lamp envelope filled with inert gas?
7. What is the diameter of a PAR30 lamp?
a. 4 3/4 in.
b. 3 3/4 in.
c. 3 in.
d. 4 in.
8. Approximately what percentage of commercial space in the US
is illuminated by fluorescent lamps?
9. A fluorescent lamp with one pin in each end is:
a. Hot cathode rapid start
b. Instant start
The design tools 65

10. What is the diameter of an F40T12 lamp?
a. 1.2 in.
b. 1–1/2 in.
c. 1 in.
d. 12 in.
11. What type of lamp is a M250/U
12. What are the two functions of a ballast?
13. You are designing HID lighting for BigBucks Inc.’s new
manufacturing facility. A 50 horsepower centrifuge is connected
to your panel. What type of ballast should you specify?
a. R
b. CW
c. HX
14. What are two purposes of reflectors?
15. Which type of diffuser would you use in a high abuse area?
a. Acrylic
b. Polycarbonate
16. How many lumens will a lamp rated 3000 lumens produce in
a luminaire having a ballast factor of 0.85?
17. What is the RCR of a 12 ft ⫻ 12 ft room which has a ceiling
height of 10 ft, and a working plane of 2 1/2 ft?
18. How many luminaires of the type shown in Figure 2.15 are
required to produce 65 fc in the space of exercise 17?
19. You want to turn off the lights in the offices of BigBucks Inc.
when nobody is in them. What type of control should you use?
a. Photoelectric
b. Occupancy sensors
c. Dimmers
20. Why do we need to be familiar with building Codes and
Standards?
Big bonus exercise
Download the VISUAL Basic Edition Tutorial from the www.litho-
nia.com/visual Web site. Print it out, and go through the tutorial
exercise. This will take you through all the features available in the
program. When you have finished the tutorial, print out your
results.
66 The Lit Interior

A space design is an accumulation of ideas coupled with a knowl-
edge of physical entities directed toward providing a particular
environment. The same can be said for lighting design, which plays
a major part in accomplishing the goals of the space designer. The
design usually begins with the architect’s concept of the ambience
of the space. This is conveyed to the lighting designer, who makes
suggestions for lighting the space based on the architect’s ideas, the
physical geometry of the space, the intended use of the space, the
intended occupants of the space, the budget for the space, and a
knowledge of the tools at his disposal.
This is likely to become an iterative process when those grandiose
first thoughts bump into the realities of budget constraints. Even
so, the design guidelines established at the first meeting with the
architect should be followed as closely as possible.
At that first meeting, the architect will present his or her ideas
to the designer, along with the floor plans for the space, and
(hopefully) elevations and sections showing wall and ceiling
construction. If not shown, the designer must ask the architect to
define the ceiling height and type for each area within the space.
This is usually done on a reflected ceiling plan, which shows the
actual ceiling plan and grid layout that the architect intends to use.
Wall and floor finishes should also be discussed, since these will
affect lighting calculations later on. If not obvious, the intended use
for each area should be discussed, as well as furniture layout, the
type of tasks to be performed there, and the average age of the
expected occupants. Finally, special effects lighting, owner’s prefer-
ences for types of specialty luminaires, and an order-of-magnitude
budget should be discussed. With all of this information firmly in
hand, the lighting designer is prepared to take a first cut at design-
ing a lighting system for the space.
Most lighting system designs include four basic types of light-
ing. These are: ambient lighting, task lighting, accent lighting, and
lighting for life safety. Let’s now take a look at each of these four
types of lighting.
3 The design process

Ambient lighting
Ambient lighting illuminates the entire space to a level which allows
intended tasks to be performed comfortably. This generally means
an even distribution of some quantity of light on an imaginary work
plane selected for the tasks to be performed. The work plane in an
office, for example, is 30 in. (76 cm) above the floor, the height of
the average desktop.
The ambient light in a space also needs to have the proper quality
to support the tasks being performed. In a space with a high use
of computers, for instance, minimizing glare is very important. If
the tasks being performed are color sensitive, such as matching
fabrics or paint, a high color rendering index (CRI) is desired.
Color is also important in creating mood: an efficient office space
needs the ‘cool’, efficient environment created by a 4100 K lamp;
a cozy restaurant needs the warm, intimate feel produced by a
2700 K lamp; and public spaces are usually best suited for the
neutral color of a 3000 K lamp. Let’s now take a specific example
and try to develop an approach to ambient lighting design.
1. Luminaire selection
Let’s say that we have just been commissioned by an architect to
provide the lighting design for a new office/conference room
addition to Bullmoose Industries’ office building. We sit down with
the architect to go over the project requirements. He presents us
with the floor plan shown in Figure 3.1.
He explains to us that the office area will have no permanent
partitions in it. The workspaces will be separated with movable
partitions, and the arrangement will be changed from time to time,
as employees move in and out. The architect says that he will select
the partitions, so we request that he select a light color, with a
reflectance value as high as possible. The architect further informs
us that the ceiling will be a suspended grid ceiling, using white
acoustical tile, 9 ft above the floor, with a 2 ft by 2 ft grid spacing
throughout the addition. With a little prodding, we discover that the
average age of the office workers will be about 45 years, and that
their work will be with normal contrast black and white text, with
a high usage of computer video data terminals (VDT). The architect
goes on to tell us that we have a moderate budget for this project,
and the client wants to put most of his money into the conference
room, which will be seen by prospective clients. The conference
room will be multipurpose, and will be used for corporate training
and board meetings, as well as for high tech presentations to those
68 The Lit Interior

Figure 3.1. Bullmoose office addition floor plan.

prospective clients. The conference room will have two company
portraits on the south wall, and a bust on a pedestal in the south-
east corner of the room.
With this information in hand, we can start to work. First, we
will select our light source for the ambient lighting of the office
space. We will use a fluorescent source, since it provides more light
for less energy input, and we can choose the color temperature and
CRI rating to suit our needs. For this application, a color temper-
ature of 4100 K and a CRI of about 75 will be adequate, since
color rendering isn’t of primary importance, and the higher CRI
lamps are more expensive.
Now we need to select the luminaire which we will be using. An
ideal luminaire for the low glare, movable partition environment of
the office space would be a suspended indirect luminaire, since
indirect lighting would be uniform throughout the space and there
would be no glare. Unfortunately, our budget and low ceiling will
not allow the use of suspended luminaires, so we are left with
troffers which fit into the ceiling grid. Now we need to find out
what is available, and what the costs are.
Here’s where we will call in the person who is going to be one
of our closest allies during the design: the manufacturer’s represen-
tative. In general, manufacturers’ representatives are highly knowl-
edgeable sales professionals who have a greater in-depth
understanding of their products than most designers can get by
skimming through catalogs. Many representatives also have well-
developed design skills. A lot of time can be saved, and a lot of
good ideas can be brought to the table by involving the manufac-
turer’s representatives early in the design.
How you find these reps is relatively easy: if you know the brand
name of a luminaire that you want to use, you can go to www.light-
search.com and search by manufacturer to get their Web address.
Then, simply go to their Web site, do a little clicking, and locate the
representative nearest you. If you have no idea of what brand will
suit your needs, you can search the lightsearch site by product
description (i.e. ‘fluorescent troffers’), and find out who makes what
you need, and then go to their Web site. For a general listing of
lighting manufacturers, you can go to www.lighting-inc.com/search-
man.html. If all else fails, you can always to go to a Web search
engine such as www.yahoo.com, and type in the generic description
of what you want (i.e. ‘fluorescent lighting’) and start visiting the
Web sites returned from your search until you find a manufacturer
who builds what you want. Then locate the representative as above.
When you contact your local rep, it helps to remember that repre-
sentatives are salesmen first and foremost, so they usually represent
70 The Lit Interior

a full line of luminaires and associated equipment. They probably
have an offering for every luminaire type that you need, and they
are happy to provide you with manufacturers’ literature and
product application guidance. In return, they expect the opportu-
nity to bid their equipment on your project.
Let’s say that our local rep has been found, has stopped by with
a few softback quick selector catalogs, and we are ready to select
luminaires. We sit with the rep and look together at the criteria for
ambient lighting of the office space:
1. the system should have low glare, because of the high use of
VDTs;
2. the system should provide even light distribution throughout the
space, because of the owner’s desire for flexibility in furniture
placement;
3. the system should provide ‘cool’ light, in order to get an
efficient ‘feel’ within the space; color rendering is of secondary
importance;
4. the system should provide adequate light for workers over the
age of 45 to perform tasks comfortably;
5. as always, the system should comply with the energy require-
ments of ASHRAE 90.1;
6. the system should fit within a moderate budget – not ‘cheap’,
but not ‘gold plated’, either.
When the lighting rep reviews these criteria, he will likely suggest
a fluorescent troffer with either a parabolic diffuser or a
direct/indirect diffuser which approximates the suspended indirect
luminaire. Fluorescent is a good choice, for reasons mentioned
previously. Troffers are suitable because of ceiling type, and the
flexibility in arrangement to provide good light distribution. Either
parabolic or direct/indirect diffusers will reduce glare. Now, if we
take a little time to reflect on the salient features of the parabolic
diffuser mentioned in Chapter 2, we will realize that parabolics are
not ideal for our application because of the sharp light cutoff that
they provide. Cutoff is beneficial in an open plan office, but when
partitions are introduced into the space, light below the cutoff angle
is blocked by the partitions, as shown in Figure 3.2. This prevents
an even contribution of light from all luminaires to the working
plane.
We will go with the direct/indirect luminaire to get the best distri-
bution possible.
We now need to select a direct/indirect luminaire that will fit into
the 2 ft by 2 ft ceiling grid of the office space. Let’s say that we
happen to have the Lithonia lighting catalog. Lithonia’s softback
The design process 71

catalog is called the Product Selection Guide, and in it we find their
recessed direct/indirect luminaire, which is called the ‘Avante’
luminaire, type AV. We see from the catalog that we have a choice
of either 2 ft ⫻ 4 ft, or 2 ft ⫻ 2 ft type AV luminaire that will fit
easily into the grid. Figure 3.3 is the catalog sheet for the type AV.
To determine which size will best meet our performance criteria,
we need to see the photometric distribution curves of each
luminaire for comparison.
The Product Selection Guide is like most manufacturer’s softback
catalogs, and doesn’t contain all the photometric distribution
curves. We can either request that the rep send us the full data
sheets for the type AV, or, we can go online and download them
ourselves. Since we’re in the twenty-first century, and have comput-
ers and all, let’s download the data.
If you remember, in Chapter 2, we downloaded Lithonia’s
VISUAL BASIC program and photometric data to perform some
calculations. Let’s go back to Lithonia’s central Web address,
www.lithonia.com, and see what we can find. When we get to the
opening screen, we see that there is a Product Info selection, which
will take us to the Online Catalog. We can click through the Indoor
and Fluorescent sections, until we find Recessed AV, which is what
we’re looking for. This will work for us, but it will take quite a bit
72 The Lit Interior
Figure 3.2. Parabolic luminaire distribution blocked by partition.

Figure 3.3. Lithonia type AV luminaire (source: Lithonia Lighting).

of time to evaluate all the photometric options for the AV. Since
we’re looking for comparative photometrics, there’s an easier way
to go. Back at the opening screen, we see a Lighting Software
section. Go there. You’ll see, among the options, a Photometric
Viewer Download. We want to download this viewer. It’s a few
megabytes, so the download may take a little while. Once the
download is finished, you’ll need to unzip the file, and install the
program according to the instructions. Now you’re ready to go.
When you bring up the viewer, you’ll see a folder called Lithonia
Photometrics, Open it, then go to the Fluorescent folder. Open it, and
go to the Architectural folder. Here you’ll see the AV folder. Open it,
and it brings up all the photometric files available for the AV
luminaire. We’re looking for a comparison between a 2 ft ⫻ 2 ft and
a 2 ft ⫻ 4 ft luminaire, so we choose a luminaire with two CF40
lamps for the 2 ft ⫻ 2 ft, and one with three 32 W lamps for the 2 ft
⫻ 4 ft luminaire. Use the Set Compare button, select the two lamps,
and hit the View button. When the photometric summary comes up,
select the CP Curve option. You’ll see the comparative photometrics
for the two luminaires. This should look like Figure 3.4.
We see two curves, one looking down the axis of the lamps,
and one looking perpendicular to the lamp axis. You can see from
Figure 3.4 that the distribution pattern for both luminaires is
symmetrical, regardless of viewing angle. This means that if either
of the luminaires were installed, and all the desks were rotated
90°, the lighting levels at the desktop would remain the same.
74 The Lit Interior
Figure 3.4. Comparison of 2 ft ⫻ 2 ft and 2 ft ⫻ 4 ft luminaire photometric curves
(source: author/Lithonia Lighting).

Either is a good choice, then, since we need flexibility of furni-
ture placement and orientation. Now what lamp should we use?
To make our final selection, we have to investigate further.
Certainly energy consumption will be one of our main concerns,
since we will have to meet ASHRAE 90.1 energy constraints with
our design. We also don’t want to encumber the client with high
energy bills, or waste the country’s valuable energy resources. In
this vein, let’s compare the lamps available to us, and see where
our best value is.
Looking at the catalog information, we see that the 2 ft ⫻ 2 ft
luminaire will accept the 40 W compact T5, the 50 W compact T5
and the 55 W compact T5. The 2 ft ⫻ 4 ft luminaire will accept
the F32T8 lamp, the F28T5 lamp, and the F54T5 HO lamp. We
have a choice of the number of lamps.
If our lighting rep has brought us a lamp catalog, we can look
up each lamp to see which has the best efficacy, or lumens per watt
in our color range. If we don’t have a lamp catalog, we can go back
to the Internet, and pull up a lamp manufacturer’s Web site. Several
lamp manufacturers have their product catalogs online, and if you
have a reasonably recent browser, you’re all set. Let’s go to the
Philips site, www.philips.com.
When we get to the opening screen, we see that we have a multi-
tude of information at our fingertips, some useful, and some not
applicable to our project. We click on the Professional Product
heading at the top of the screen, and select Lighting, because that’s
what we’re interested in. Under lighting, we see catalogs, and we
have a choice of their European or North American offerings. We’ll
select North American, and we see that there is a Full Lighting
Product Catalog available. This is Philips’ on-line catalog. Click on
that. We can download the entire catalog, and have it on hand for
future projects, or we can just retrieve the information we need,
and get on with the job. For now, we’ll just get what we need.
Under the Advanced Search section, in the ‘Lamps’ window, select
compact fluorescent, and click on search. Philips’ entire line of
compact fluorescent lamps will be returned. Scroll through offer-
ings down to 50W, and you’ll see several 50W PL-L long fluores-
cent lamps. That’s what we want. The ‘long’ indicates that the lamp
is 24 inches long. Each offering is for a different color temperature.
If you select the first lamp, you’ll see that it is 4100K, which is
what we want, with an initial lumen output of 4300 lumens, and
a CRI of 82. The listing also includes ‘design lumens’, which is the
initial lumens multiplied by the Lamp Lumen Depreciation (LLD).
The 50W lamp appears to fit our needs. Now, in order to find the
40W lamp, we’ll refine our search efforts somewhat.

Back-up to the search menu and again select compact fluorescent.
This time, pick the ‘watts’ scroll arrow, and scroll down to 40W.
Philips doesn’t offer a 40W lamp. The closest to it is a 38W lamp.
Select that, and only the 38W offerings are returned. Select the first
one, and you’ll see that it has an output of 3300 lumens, a color
temperature of 4100K, and a CRI of 82. Also a good choice. Now
go back to the search menu, select Fluorescent, 32W, and T8 for tube
type. This zeros right in on the lamp we are looking for. We select
the 4100K offering, and find that it has an initial lumen output of
2950 lumens, and a CRI of 86. Another winner. We could go through
the same process and obtain the data for our T5 lamps, the 28WT5
and the high output, F54T5 HO, but the T5 lamps are expensive,
and not readily obtainable in some places, so we’ll deem them not
suitable for our purposes. T5 lamps are very efficient, however, and
should be considered for projects which will be maintained profes-
sionally. One thing to remember is that the high output F54T5 HO
lamps produce so many lumens (5000), that they can only be used
in indirect luminaires, where the source is not visible.
Now we have all the lamp data we need to see which lamp best
fits our needs, so let’s look at the efficacies (lumens per input watt
ratio) for each of our selected lamps using initial lumens.
For the 50W compact fluorescent, efficacy is 4300 lumens/
50W=86; and for the compact 40WT5, we have 3300 lumens/
40W=82.5, and for the F32T8, efficacy is 2950 lumens/32W=92.
Clearly, the lamp with the best efficacy in this lot is the F32T8
lamp, so we would like to use F32T8’s if the design will allow. Any
of these lamps will operate efficiently on an electronic ballast,
which we will use to eliminate flicker.
Now we have two luminaires complete with lamps and ballast
that we can use to provide ambient lighting for the office space.
The question is, how many of each of these luminaires will we need,
and where should they be placed?
To determine the number of luminaires, we first need to deter-
mine the number of footcandles we need on the desktops in the
space. This requires going to the IES-recommended footcandle tables
and looking up our space. The proper classification for our space is
open plan office with intermittent VDT use. If we look back at
Figure 2.18, we see that our office falls into category E, which corre-
sponds to a value of 50 footcandles (50 fc). For a first cut at deter-
mining quantities of each type of luminaire, we can run some zonal
cavity calculations. If you don’t remember the zonal cavity calcula-
tion procedure from Chapter 2, now would be a good time to take
a couple of minutes for review. Or. . . we can run our zonal cavity
calculations using that nifty photometric viewer program that we
76 The Lit Interior

just downloaded. For those of you who enjoy grinding through the
math by hand, have fun. You have all the data needed to evaluate
a 2 ft ⫻ 4 ft luminaire with two, and three lamps, and a 2 ft ⫻ 2 ft
luminaire with two 40 W lamps. Our office space is 20 ft ⫻ 20 ft,
with a 9 ft ceiling, and a work plane 2.5 ft from the floor.
O.K. – just to humor the math whizzes among you, here’s how
the zonal cavity calculation would go for the 2 ft ⫻ 2 ft luminaire
with two CF40W lamps:
Room cavity ratio, or RCR =
5(6.5) ⫻ (20 ft + 20 ft)
= 3.5
(20 ft ⫻ 20 ft)
We can pull up the photometric viewer, and find our coefficient of
utilization (CU) is 0.5. We use a generic electronic ballast factor of
0.80, and since an office is a relatively clean environment, a
luminaire dirt depreciation (LDD) of 0.90. That gives us a total
light loss factor (LLF) of 0.9 ⫻ 0.8, or 0.72. Use the design lumens
of 2970 to account for LLD, and for the desired 50 fc, we have:
Luminaires =
50 ⫻ (20 ft ⫻ 20 ft)
= 9.35
2(lamps) ⫻ 2970 ⫻ 0.72 ⫻ 0.5
For the rest of us, let’s look back at the photometric viewer and click
on the AV luminaire. Then let’s select the 2AVG2CF40ADP
luminaire. That’s the one with two CF40 lamps. Next, hit the View
button to bring up the photometric summary. This time, we will
select the Room Estimator option. The estimator asks us to fill in the
room dimensions, and the luminaire mounting height. The viewer
provides default working plane height, lamp lumens, and light loss
factor. The RCR, and CU are also provided by the program, having
been calculated from room data input and stored luminaire data. We
can type in the desired footcandles at 50, and the program runs a
zonal cavity calculation to show that we need. . . What? 6.2
luminaires? Why is this so different from the 9.35 luminaires that we
calculated by hand? Let’s go back and look at the estimator screen.
The default LLF is 1.0, which doesn’t take into account the ballast
factor, or the LDD, which brings our LLF down to 0.72. We type
that in, and see that we still only need 8.7 luminaires. The program
also defaults to 3100 lumens/lamp, which is lamp initial lumens. If
we go back and plug in the design lumens of 2970, we see that the
required luminaires goes to 9.2, which is close enough.
This is a good point to remember. When using quick calculator
computer programs, always check to make sure that the default values
make sense. We know that the LLF is always less than 1.0, and that we
use design lumens to assure better system performance over the long run.

Now let’s run the program for the 2 ft ⫻ 4 ft luminaire, with
both two and three F32T8 lamps. The program will retain our
inputs, so all we need to change is the lamp photometrics, and the
LLF to a more reasonable value of 0.65. After a bit of mousework,
we see that we need 9.4 of the two-lamp luminaires, and 6.7 of the
three lamp.
If cost was our major concern, the quick estimator would suffice,
and at this point we would choose to go with six of the three lamp
luminaires. But we have light distribution as a major concern, so
we will now have to run point-by-point calculations to see how our
three choices perform. The easiest way to do this, of course, is by
using the computer, so now we will pull up the VISUAL BASIC
program that we downloaded in Chapter 2.
We will enter the geometry of the room, the ceiling grid type, use
standard reflectances, and select the photometric file for the luminaires
and lamps that we have chosen. Below the photometric file selector is
a light loss factor selector which offers either standard or IES calcu-
lated light loss factors. None of the standard values fit our needs, so
click on the icon beside the ‘LLF Value’ window. For the 40 W compact
fluorescent lamp, we will use ‘fluorescent’ and ‘T5 Long CF’. For the
78 The Lit Interior
Figure 3.5. Bullmoose office VISUAL results using (a) 9.2CF40 luminaires, (b)
9.2F32T8 luminaires, and (c) 6.3F32T8 luminaires.
(a)

(c))
(b))

F32T8s we will use ‘Fluorescent’ and ‘T8 Rapid Start’. Both lamps
have a calculated LLF of 0.9. Continue on through the windows: For
LDD we will use ‘Indirect Luminaires’; and for the ballast we will use
‘Electronic’. None of the ‘other’ factors apply to our situation. We are
now left with a combined LFF of 0.61. Now run the calculator using
a desired illumination of 50 fc for each luminaire.
As the results come up for each luminaire type, make a note of
the calculated power density for later comparison with the
ASHRAE 90.1 allowances. Make a calculation run for each of the
three types, using the ‘Tools’ menu, and the ‘Lumen Method’ button
to return to the calculation program to change lamps. The program
will retain the other settings. When you have finished, the results
should look like Figure 3.5a–c.
The first thing that we notice about the results is that the average
footcandles computed for the six 3F32T8 luminaires is more than
that for the nine 2CF42 luminaires, and about equal to that of the
nine 2F32T8 luminaires. The max/min ratio is seen to be better for
the six three-lamp luminaires, which indicates a better light distri-
bution. The higher the ratio, the less uniform the light, and vice
versa. Further examination shows that the six three lamp luminaires
provide approximately 50 fc in the central three-quarters of the
room, where the work will most likely take place. This is a good
distribution of light, and the lamps with the highest efficacy are
being utilized. We will use the six 2 ft ⫻ 4 ft luminaires with three
F32T8 lamps each. It is interesting to note again, that at no point
on the grid do we get 47.1 fc, which was our average illumination,
and what we would expect from a zonal cavity calculation. As you
become more accustomed to computerized lighting calculations,
you will probably abandon zonal cavity calculations altogether, and
instead utilize the more advanced programs, such as VISUAL PRO,
which will allow you to model spaces much more accurately.
Energy code compliance
OK, now that we have settled in on luminaires for the office, let’s
run a quick ASHRAE 90.1 check to make sure that the power
density is within the guidelines.
From Figure 2.17 in Chapter 2, we can see that our power
density allowance for this space is 1.3 W per square foot, or 520 W
for the whole 400 sq. ft space. We can look back at the notes we
took during the calculations and see that the power density for the
six 3F32T8 luminaires is 1.3, so we are just within the guidelines.
Our notes show that the other two options exceed 1.3 W/sq ft, and
are not within the guidelines. We have made a good choice.
80 The Lit Interior

Figure 3.6. Lithonia type SP luminaire (source: Lithonia Lighting).

Now let’s look at the hallway, which also requires ambient light-
ing. Hallways, or paths of egress, are required by code to have illumi-
nation of 10 fc at the floor. No visual tasks are being performed there,
so glare and color rendition are of minimal concern. Ten footcandles
doesn’t represent many watts/square foot, so if we have reasonable
efficacy, we’re not likely to get into trouble with the energy code. This
means that a ‘plain Jane’ luminaire will suffice. Looking back at our
catalog, we see the 2 ft ⫻ 2 ft troffer shown in Figure 3.6.
This luminaire has an acrylic diffuser, and will fit nicely into our
ceiling grid. We want to use a 3000 K lamp here, to produce a
‘neutral’ feel to the space and we’ll use the 40 W compact fluorescent
lamp because of the efficacy. To calculate the number of luminaires
required to produce the 10 fc, we can return to the computer. This
time, the working plane is at 0 in. (the floor). Running the program,
we find that we can get 10 fc with only one luminaire. This would
make our hallway look like a cave, so we’ll try two luminaires and
see what happens. The VISUAL results are shown in Figure 3.7. The
light distribution is fairly even, and we have more than the required
10 fc, so we’ll consider this a good fit, and move on.
Now let’s take a look at task lighting for the conference room.
82 The Lit Interior
Figure 3.7. Bullmoose hallway VISUAL results.

Task lighting
Task lighting means putting the light where you need it to do the
job. This infers that task lighting is almost always direct lighting.
If we look at the conference room in Figure 3.1, we can see a couple
of areas where task activity will take place: the conference table, of
course, where everybody will be sitting; and the side table area,
where people will refill their coffee cups from time to time. Now,
how should we light these areas?
If we look back at our criteria for the conference room, we see
that we need enough light on the table to be able to perform detailed
work in training sessions (60–70 fc), but we need only enough light
to take notes (10–20 fc) when a presentation video is in use. The
same is true for the side table: when everybody is up getting coffee
and pastries, they need to see what they’re doing; when the video is
on, you only need minimum light in that part of the room.
This situation will be accommodated by putting dimming
controls on the luminaires that we use for the table and the side
table. Now what luminaires should we use?
Luminaire selection
Again, for color temperature, CRI, and amount of light produced,
we should consider fluorescent first for the lighting of the confer-
ence table. We will mount the luminaires directly over the confer-
ence table, since that is where the tasks will be performed. The
spacing of the luminaires should offer even light distribution on the
entire surface of the table, and glare should be minimized. There are
no partitions involved in this application, so parabolic diffusers
should work well – perhaps better than the direct/indirect
luminaires, because light trespass into areas other than the task area
will be limited by the cutoff characteristics of the parabolic diffusers.
This time, instead of calculating a number of luminaires required
to provide a specific light level, we will locate our luminaires
directly above the task area, and space them evenly to provide good
light distribution. If we look at the geometry of the conference
table, we see that three 2 ft ⫻ 4 ft luminaires will fit nicely into the
ceiling grid above the table. The long axis of the luminaires will be
parallel to the line of vision of those sitting at the sides of the table,
which will further reduce glare for the majority of those at the
table. If necessary, we can adjust the maximum light output of the
luminaires by choosing the number of lamps in the luminaires. We
now go back to the catalog to select the luminaire. Figure 3.8 shows
the catalog data for an appropriate parabolic luminaire selection.

84 The Lit Interior
Figure 3.8. Lithonia Type PM4 luminaire (source: Lithonia Lighting).

A zonal cavity calculation for the area above the table wouldn’t
have much meaning, but we can run the computer analysis for that
area. We assume that our space stops at the boundaries of the table,
and that the wall reflectance is zero. This time we use the feature
of the program which allows us to place the luminaires where we
want them. First, let’s try three F32T8/841 lamps per luminaire.
Figure 3.9 shows the results of the computer run.
We can see that three lamps per luminaire will give us about 99 fc
in the center of the table, and an average of 78 fc. This is about
right for maximum illumination for close work at the table. We’re
going to use dimming ballasts on these luminaires, so we can reduce
the level for less intensive tasks. Now, what about the side table?
Let’s take a look at how we want the side table lighting to function:
it must provide enough light to operate a coffee pot; it must be
dimmable to reduce brightness during presentations; and we also
don’t want to be able to see the source of light while seated at the
conference table. Because of the room layout, we can see that troffers
aren’t suitable for this job. Looking back into our toolbox from
Chapter 2, we can see that a recessed downlight will give us direct
lighting, and also hide the light source. We must go back to our
Figure 3.9. Bullmoose conference table VISUAL Results.

86 The Lit Interior
Figure 3.10. Lithonia type AF luminaire (source: Lithonia Lighting).

catalog and find a downlight which suits our purpose. The catalog
specification sheet for one such luminaire is shown in Figure 3.10.
A word of caution here: when selecting recessed downlights,
always find out whether insulation is to be installed above the
ceiling in which the luminaire is mounted. If it is, you must use an
‘IC’ (insulation contact) rated luminaire, or you will have excessive
heat buildup.
Fortunately, the ceiling in our conference room has no insulation
above it, so we can use a non-IC rated luminaire. We will use a
fluorescent lamp, so that we may match the color of the lamps over
the conference table, and we will use a dimming ballast to dim the
luminaire when desired. Horizontal lamp mounting will be selected,
so that the lamp will not be visible when the luminaire is viewed
from an angle. To further camouflage the light source, we will use
a black grooved baffle trim on the inside of the luminaire.
Our selected luminaire offers a 42 W triple tube compact fluores-
cent lamp as an option, so we will use this to get as much
undimmed light as possible out of the luminaire. No particular
footcandle level is required here, so three luminaires, mounted
directly above the side table, should suffice.
Even though there is no furniture shown on the east wall, there
is a big open space there, so there’s a pretty good chance a
telephone table, or something else, will eventually be put there. We
will put two downlights over that area just for good measure.
We now have the task areas lit, so what else do we need? If we
look around, we see a presentation easel in the front of the room,
the company portraits on the back wall, and the bust of
Commodore Bullmoose himself in the back corner. It would be nice
to accent these features with light, so let’s see what we can do.
Accent lighting
Accent lighting, like task lighting, is direct lighting projected on a
specific area for a specific purpose: Task lighting illuminates an area
so that a task may be performed there; accent lighting illuminates
an object so that it may be seen clearly and dramatically.
The majority of accent lighting that we encounter in the real
world is done from above, with ceiling-mounted luminaires. Most
of these luminaires, particularly in retail spaces, are track mounted.
Track lights are versatile, easily adjusted, and easily re-lamped to
perform a variety of accent lighting jobs. In our conference room,
however, the architect feels that a surface-mounted track would
‘clutter’ his ceiling, and take away from the effect that he is trying

88 The Lit Interior
Figure 3.11. Lithonia Type DLV luminaire (source: Lithonia Lighting).

to achieve. We must go back to the catalogs to find a recessed,
adjustable downlight that will accommodate the type of lamps that
we require for accent lighting. The catalog data for one such
luminaire is shown in Figure 3.11.
The luminaire shown in Figure 3.11 is available in adjustable
accent and wallwash accent configurations. It is designed to utilize
the MR-16 low voltage lamp, which, as you should remember from
Chapter 2, produces a brilliant, focused white light in several beam
spreads. It is also very hot, but as said before, we have no insula-
tion concerns in our space.
The rule of thumb for wallwashing in general is to space the
luminaires equally from the wall and each other to obtain uniform
illumination. In our case, we are using the wallwashers for accent
lighting, so we will mount a wallwash luminaire in front of each of
the portraits, so that the light strikes the portrait at an angle of 30°
or less from the vertical. This is to prevent glare from the glass cover-
ing of the portraits. The mechanics of this is illustrated in Figure 3.12.
This will give us an oval of light on the portrait for an accent
effect. The lamp position and beam spread are both selectable, and
may be adjusted to frame the entire portrait. For our presentation
easel, we will mount one of the accent downlights so that we can
frame the entire presentation surface and maintain our 30° angle.
For our pièce de résistance, we will locate two downlights over the
bust of the Commodore, to accent his chiseled features and give
Figure 3.12. Accent luminaire mounting.

him a three-dimensional appearance (remember ‘light and shadows’
from Chapter 1). Again, these downlights should be placed so that
the light hits the sculpture at an angle of 30° or less from the verti-
cal to eliminate glare from the Commodore’s prominent proboscis.
All of the accent luminaires will be adjusted after installation to
maximize their effect.
Finally, we will put dimmers on the accent lights so that they
may be dimmed while presentations are taking place, and that
about wraps it up for the new spaces – or does it?
What happens if the electricity goes off just when Bullmoose, Inc.
has a conference room full of foreign investors? Those guys will be
crashing around in the dark, trying to find their way out of unfamil-
iar surroundings, and not feeling very benevolent toward Bullmoose,
Inc., unless. . . unless we have done a good job of lighting for life safety.
Lighting for life safety
Lighting for life safety means providing enough light for occupants
to safely exit a building in case of a power outage, which often
accompanies a fire in the building. It also entails guiding those
occupants out of the building by the use of exit signs.
The Life Safety Code (NFPA 101) requires that we provide an
average of 1 fc at the floor on the paths of egress from the building
in emergency conditions. Power for the emergency lighting can either
be provided by a backup battery system, or an emergency generator
with an automatic switch to transfer loads from the normal to the
generator source. Battery systems can be purchased in two configu-
rations: a centralized battery, charger, and transfer switch that powers
a number of emergency luminaires; or individual batteries, charger,
and transfer switch located within the luminaire itself. Most fluores-
cent luminaire manufacturers offer the emergency backup option, up
to 1100 lumens per luminaire, as a standard package.
The Bullmoose building has no emergency generator, so that
option is out for us. A centralized battery system is best suited for
a large area in which a number of emergency luminaires are
required, but would not be cost-effective for our small area, which
will use only a few emergency luminaires. We are left with provid-
ing battery backup in a few selected luminaires in our space. Now,
which luminaires should we choose?
Emergency lighting design is about 90% ‘feel’, and 10% calcula-
tion, if any calculation at all is required. Since 1 fc is very easy to
obtain, we can place luminaires equipped with emergency packs
almost anywhere within our small spaces and get there. In our case,
90 The Lit Interior

Figure 3.13. Bullmoose office addition lighting layout.

we need to think about the intent of the code, rather than the letter
of the code, in order to do a good job of lighting for life safety. The
code stresses that the paths of egress be illuminated. This means that,
were you inside the space when the power went out, you would need
enough light to safely exit the space without tripping over something.
Let’s look at the office space. We have six luminaires spaced evenly
in the ceiling. It would make sense to provide emergency lighting in
the back of the room, farthest from the door, since the workers there
have more obstacles in their path of egress. It also makes sense to
put emergency lighting near the door, so the way out can be clearly
seen. We can use two emergency luminaires and have the office space
well covered. Now for the conference room, where all those foreign
investors are watching a corporate presentation. We’ll use a little
overkill here, since it is important that the guests feel comfortable,
even in the event of a power outage. We have three 2 ft ⫻ 4 ft
luminaires above the conference table, so we will put battery backup
in the two outboard ones. That will provide plenty of light. Out in
the hallway, where everybody will be, once they leave their rooms,
we need to provide both illumination and direction to the way out.
We will provide battery backup in the luminaire closest to the door,
and an illuminated exit sign with battery backup above the door
leading to the outside. The exit sign will be illuminated by an LED
(light emitting diode) source because of the low wattage and long
lifetime of the LEDs. This should lead everybody out safely.
Now our layout for Bullmoose, Inc. is complete. Next, we need
to identify the luminaires that we have used. To do this, we have
assigned a luminaire type for each of the luminaires in our layout,
and these are shown in the final layout of Figure 3.13.
92 The Lit Interior
Table 3.1. Luminaire schedule.
Type Manufacturer Volts Catalog no. Lamps Ballast Comments
A Lithonia 120 2AVG332 ADP 120 3-F32T8/741 2-2F32 Elect Office double
sw
AE Lithonia 120 2AVG332 ADP EL 120 3-F32T8/741 2-2F32 Elect W/emerg batt
pack
B Lithonia 120 2SP2CF400A12 120 2-40WTT5 Electronic Hallway
BE Lithonia 120 2SP2CF40A12EL 120 2-40WTT5 Electronic W/emerg batt
pack
C Lithonia 120 2PM433218L 120 3-F32T8/741 Elec dimming Conf table
CE Lithonia 120 2PM433218L EL 120 3-F32T8/741 Elec dimming W/emerg batt
pack
D Lithonia 120 LGF 42TRT 75B 120 ADEZ 4-2WTRT Elec dimming Side table
E Lithonia 120 DLVADJ MR’16 4ACT30 120 7-5WMR16 MF Accent-easel
F Lithonia 120 DLV WSH MR16 4AC 120 7-5WMR16 FL Wallwash
G Lithonia 120 DLVADJ MR’16 4ACT30 120 7-5WMR16 NS Accent-bust
X Lithonia 120 LE S W 1 R 120ELNSD Red led exit
Adapted with permission from Bullmoose, Inc.

Now we need to prepare a luminaire schedule, which will
tabulate the luminaires that we have selected. The schedule should
list each type of luminaire, and contain all pertinent information
on the luminaires that we have chosen. Table 3.1 is a good format
for the luminaires in the Bullmoose project.
All we have to do now is send the architect an invoice for our
services, and then go out and party, right? Not quite. We still have
to figure out how to make the design work, and put it all on a set
of plans, so that a contractor can build it.
The next chapters will help us to do this. First though, let’s try
a few of those fun exercises to see what you have remembered from
this chapter.
Exercises
1. What do you need to know about a space before you can begin
lighting design?
2. What are the four basic types of lighting?
3. What does ‘work plane’ mean in ambient lighting?
4. What temperature lighting would normally be used for ambient
lighting in a restaurant? Why?
5. If there were no constraints, which type of luminaire would you
choose for low glare and even ambient light distribution?
6. What is a lighting manufacturer’s representative, and why is he
or she important to our design efforts?
7. What does it mean when the parallel and the perpendicular
photometric curves of a luminaire are almost identical?
8. What is the efficacy of a CF40T5/741 lamp with an output of
3300 lumens?
9. Would a layout with a max/min ratio of 2.5:1 provide better
light distribution than one with a max/min ratio of 1.5:1? Why?
10. How many footcandles at floor level are required for hallways?
11. What is the purpose of task lighting?
12. What does ‘IC rated’ mean for a recessed downlight?
13. What type of luminaire provides the majority of accent lighting
in retail spaces?
14. How many footcandles do we need on the paths of egress
during emergency conditions?
15. When would we use a centralized battery system for emergency
lighting?
16. What are the two things we are trying to accomplish with
emergency lighting?
17. Why do we specify an LED source in exit signs?

Now that we have selected the luminaires, and put together the
layout for Bullmoose, Inc., we need to make the system function.
To accomplish this, a number of decisions must be made, some of
which could influence or negate our wonderful layout. The process
of lighting design, as stated before, is an iterative process that offers
the best compromise between the artist’s vision and the real world.
Let’s look now at some of the components involved in the power
and control of lighting in general, and then we’ll get back to the
Bullmoose project.
Power
System voltage
One major concern is the voltage available to power the lighting
system. Power companies in the US have standardized on three
delivery voltages for buildings. These are 480Y/277 V three phase,
208Y/120 V three phase, and 240/120 V single or three phase.
Larger buildings will typically have three-phase power available to
drive the large heating and cooling loads, while smaller buildings
often are served only with single-phase power.
Lighting loads are all single phase, so the lighting designer has
the choice of 277 V or 120 V. Except in rare cases, incandescent
lighting will only operate on 120 V, so if the building is served with
480Y/277 V, a step-down transformer must be used to power incan-
descent luminaires. We must then evaluate the economics of
installing the transformer versus going to a ballasted light source,
such as fluorescent or high intensity discharge (HID) lamps, which
will operate on either 277 or 120 V.
Often, in a large project, 277 V is more economically attractive
than 120 V, and to see how this works, let’s consider how the
system will be wired.
4 Powering and controlling the
system

Wire sizing
Standard practice is to limit the size of the wiring serving lighting
loads to No. 12 AWG, because anything larger than No. 12 is diffi-
cult to connect inside a luminaire, and labor costs increase dramat-
ically (as do muttered insults by contractors) when larger wiring is
used. No. 12 wire is rated for 25 A current load by code, and this
limits the number of luminaires which can be connected to a circuit.
To complicate matters further, the circuit must be protected by a
20 A molded case circuit breaker, which can only be loaded to 16 A
by code. Each lighting circuit, therefore, is limited to 16 A load.
A quick review of the basic electrical relationship P = I ⫻ E will
reveal that for the allowable load of 16 A at 120 V, only nineteen
100 W luminaires can be connected on a circuit, while 16 A at
277 V will allow forty-four 100 W luminaires to be connected. If
you’re not up on electrical relationships, P is power in watts, I is
current in amps, and E is voltage. Simply put, watts equals amps
multiplied by volts.
It’s easy to see that where the objective is to serve the maximum
number of luminaires with the least number of circuits, 277 V
would be the choice. This is applicable where it is desirable to serve
large areas, such as open office spaces, by a single panelboard,
which is limited to 42 breaker spaces by code.
Panelboards
Panelboards which serve lighting loads are standard circuit breaker
panels, mounted either flush into, or on the surface of a wall. The
panelboard assembly consists of a metallic box, called a can, which
houses an interior section consisting of vertical busses, to distrib-
ute power, circuit breakers to serve the individual loads, and termi-
nation blocks for neutral and grounding connections. A three-phase
panel contains three vertical busses, and a single-phase panel
contains two busses.
The circuit breakers either snap or are bolted onto the busses to
provide the power, or ‘hot’ connection for the lighting circuit. The
circuit breakers are designed to automatically open the circuit in
the event of overcurrent, and also serve as an on–off switch for the
circuit. The final element of the panelboard is the cover, which
contains a lockable door to keep the public out of the circuits, and
which also trims out the opening made for the can.
Lighting loads may be directly controlled from the panelboard
itself if a special switching duty circuit breaker, called a SWD
breaker, is used. This is useful in large areas, such as in open plan
office spaces, where it is desirable to switch large areas as a block
Powering and controlling the system 95

load. In these cases, SWD breakers of either one, two, or three poles
may be used to control the power from two or three panelboard
busses simultaneously. For example, 132–100 W luminaires could
be switched together using a three pole, 277 V, 20 A switching duty
breaker, with 44 luminaires connected to each of the three panel-
board busses.
It is always a good idea, when using a three-phase panelboard,
to distribute the lighting loads as evenly as possible between the
busses. This is called ‘balancing the load’. Unbalanced loading can
create large neutral currents and overheating within the panelboard.
Figure 4.1 illustrates how the individual circuit breakers are
connected to the busses in a three-phase panelboard.
Balancing the loads is an iterative operation that is most easily
accomplished through the use of a panel schedule, such as the one
shown in Figure 4.2.
Lighting loads are assigned to the busses sequentially, and then
the total bus loads are calculated by adding the individual loads
together. If the bus loads significantly differ from one another, the
designer must reassign the loads until balance is obtained.
96 The Lit Interior
Figure 4.1. Three-phase panelboard diagram.

Figure 4.2. Three-phase panelboard schedule.

Load calculations
To calculate incandescent loads, we only need to add up the wattage
of all the luminaires connected to the circuit. If amp loads are
desired, total wattage divided by voltage (120 or 277) yields amps
load. Ballasted loads are somewhat different in that a power loss
associated with the ballast must be included in the total. For fluores-
cent fixtures with magnetic ballasts, this loss will be approximately
10% of the lamp wattage. For example, a fixture containing two
34 W F34T12 lamps would present a load of 110% of (2 ⫻ 34 W),
or 75 W. Fluorescent fixtures operating on electronic ballasts,
however, often present a load of less than the combined wattages of
the included lamps. This is because the electronic ballast, which
turns on and off at high frequency, is ‘off’ a lot of the time. Typically,
a fixture containing two 32 W F32T8 lamps would present a load
of only 56 W. High intensity discharge ballast losses vary with the
type and wattage of lamp. It is always advisable to consult the
manufacturer’s information when calculating HID loads. In all cases,
single-phase lighting amp loads can be found by dividing the total
luminaire wattage by the voltage across the load (I = P/E).
Wiring and raceways
Because of circuit breaker restrictions, the amp load on a single
20 A circuit breaker cannot exceed 16 A. This is safely within the
25 A allowed by code for a No. 12 AWG copper conductor wiring
system. Copper conductors should always be used for lighting
wiring systems, because of the corrosion and temperature problems
associated with aluminum conductors.
Wiring insulation, or the jacket covering the copper conductor,
is typically either rubber, denoted by an ‘R’ in the wire type desig-
nation, or thermoplastic, denoted by a ‘T’. Thermoplastic insula-
tion is thinner than the rubber, so the overall cable diameter is less
in a ‘T’ type cable. The ‘T’ type cable allows more cables to be
pulled in a given size conduit than the ‘R’, and generally results in
lower job cost. For this reason, type ‘T’ insulation is recommended
for lighting jobs requiring conduit.
Some luminaires generate a considerable amount of heat, so the
wiring insulation has to have the ability to withstand heat. This
capacity is denoted by an ‘H’ or ‘HH’ in the wire type designation,
such as ‘THHN’. The NEC table 310-16 lists three categories of
temperature ratings for wiring insulation: 60, 75, and 90°C. For
almost all lighting applications, the 75°C wire is adequate. In rare
cases, such as enclosed high power fiber optic sources, 90°C wiring
insulation is required.
98 The Lit Interior

Figure 4.3. NFPA-70 (NEC) ampacity table (source: NFPA).

The building codes for commercial installations usually require
lighting circuits to be pulled through conduit. If the pulls are diffi-
cult, or extremely long, an overall nylon jacket is available to
protect the insulation from damage. This is denoted by an ‘N’ in
the wire type designation. Finally, to protect against condensate, or
moisture in the conduit, the cable should be rated for wet applica-
tions. This is denoted by a ‘W’ in the type designation.
Fortunately for lighting designers, almost all cable manufacturers
make a type THHN/THWN cable, which is ideally suited for light-
ing applications. Note: residential installations, which do not require
conduit, are normally wired with type NM (Non-Metallic sheathed)
cable. Type NM is only rated for 60°C, and could cause problems
with high temperature luminaires. Since we are primarily concerned
with commercial installations, we will only use 75°C wiring pulled
in conduit. Figure 4.3 is the NEC ampacity table, which lists current
carrying capacity of type THHN/THWN wire in conduit.
The conduits through which lighting circuits are pulled are
nothing more than pipes, and they are manufactured from several
materials, each having a special purpose. Underground or in-slab
conduit runs utilize PVC (polyvinyl chloride) conduit because of its
resistance to corrosion. Conduit runs inside the structure are made
in electrical metallic tubing (EMT) for mechanical protection, and
also to provide electromagnetic shielding for sensitive equipment.
In extremely harsh environments, such as in heavy industrial plants,
circuits may be run in PVC-covered metal conduits.
Lighting circuits are usually run in hard conduit to a junction
box in the immediate vicinity of the luminaires served. The wiring
from the junction box to the individual luminaires is run in flexi-
ble metallic conduit (greenfield) for ease of connection. The code
allows six feet of flexible cable to be used for this purpose. Figure
4.4 is a NEC table that specifies the maximum number of wires
that may be pulled in a conduit.
Lighting controls
After the luminaires have all been selected and arranged within the
space, it’s time to consider how the system will be controlled to
offer the occupants the most beneficial use of the space.
Switches
The most common form of lighting control is by the single pole,
manually operated toggle switch. Switches are typically located
100 The Lit Interior

within the space to be lighted, usually on the lock side of the entrance
door, mounted 48 in. (122 cm) above the floor. If there is more than
one door leading into a space, three-way, and four-way toggle
switches are available to allow switching from any door location.
Figure 4.5 contains connection diagrams for toggle switching.
Figure 4.4. NFPA-79 (NEC) conduit allowable fill table (source: NFPA).

Switches are available for both 277 V and for 120 V, and are
available in either 15 or 20 A ratings. The 20 A switches have
slightly heavier contacts, and their use is recommended. The total
luminaire amperage on a circuit cannot exceed the switch rating,
so if you push the circuit to its full 16 A capacity, you must use
20 A rated switches.
Toggle switches are either on or off, and have no light dimming
capability. When used in conjunction with multi-ballasted fluores-
cent fixtures, however, they can offer some lighting level control.
Figure 4.6 is a connection diagram of a double-switched, two-
ballast, three-lamp fluorescent luminaire that provides three light
levels: one, two, or all three lamps can be illuminated by the use
of the two toggle switches.
Dimmers
When continuous dimming of the light level is desired, such as in
churches, restaurants, theaters, etc., specialized dimming equip-
ment, tailored to the luminaires to be dimmed must be used. Since
Figure 4.5. Single and three-way switching.
Figure 4.6. Double-switched three-lamp luminaire.

dimmers are much more expensive than on–off switching, econom-
ics will often dictate the type and amount of dimming used.
Dimmers do as their name implies: they dim, or reduce the light
output of the luminaires attached to them. The type of dimmer
most widely in use today is the simple rheostat, or variable resis-
tor, which is used to dim incandescent loads. Rheostats directly vary
the amount of current flowing through the incandescent filament,
and by doing so, they vary the light output of the lamp. Rheostats
are line voltage, and come in various sizes, which indicate the
maximum amount of wattage that they are capable of controlling.
Common rheostats are available up to 2000 W, which is the
maximum load that can be put on a 20 A circuit at 120 V.
Dimming a fluorescent luminaire requires a special dimming
ballast. Magnetic fluorescent dimming ballasts operate from line
voltage, and are normally used in conjunction with a single circuit,
wall-mounted dimming control. Electronic fluorescent dimming
ballasts are controlled by a separate low voltage dimming circuit,
usually 24 V. This arrangement is usable with locally mounted
controls, and is also suitable for zone control of block loads. This
is particularly applicable to computerized dimming control that
offers multiple preset ‘scenes’ such as that used in churches and
performing arts theaters. In operation, this system allows the user
to set the level of several groups of luminaires through the use of
slide or rotary switches, and then ‘save’ the settings as a scene. To
recall a scene, the user needs only to push a single button, and the
saved settings are automatically retrieved by the dimming system.
If groups of high wattage luminaires are to be dimmed, such as
in large churches or theaters, specialized dimming systems capable
of handling large power loads are used. These systems are designed,
building block style, from rack-mounted components specifically
selected for the purpose.
Contactors
When it is desired to control a larger group of luminaires than a
single-switched circuit can handle, and multiple switches are
undesirable, as is common in large office spaces, lighting contac-
tors are used. Contactors are essentially solenoids, or relays, in
which a low power coil actuates, or ‘pulls in’ a set of heavy contacts
that applies power to the lighting load. The coil itself can be
activated by a single manual control device such as a wall-mounted
toggle switch, or it may be activated by automatic controllers, such
as photocells, occupancy sensors, timers, or building management
computer systems. Contactors typically have from 2 to 12 sets of

contacts, rated at 30 A each. Larger contactor ratings are available
for specialized purposes. Each set of contacts can be used to power
a separate lighting circuit.
Once activated, contactors are either mechanically or electrically
held in the closed position. In the mechanically held contactor, the
mechanism closes when the coil is activated, and it is held closed
by a mechanical ‘latch’ until a second coil is activated, which
‘unlatches’ the mechanism. This requires only a momentary appli-
cation of coil power through the switching device. The electrically
held contactor requires that coil power be continuously applied
while the contactor is closed. Removal of coil power allows the
spring-loaded contactor to open. The electrically held contactor is
less expensive than the mechanically held, but it can produce an
undesirable buzzing sound while the coil is energized.
Photocells
Photocells are basically devices used to turn the lights on when it
is dark, and to turn them off when daylight is present. A photocell
consists of a photovoltaic cell connected to a current-sensitive relay.
When light strikes the cell, an electric current proportional to the
intensity of the light is generated. When that current is sufficient to
activate the relay coil, normally closed relay contacts open, and
interrupt the power to a lighting circuit or contactor. When low
light is present, the contacts close, and apply power to the lighting
circuit. The contacts are normally rated for only 5 or 10 A, so the
photocell can directly control only a small number of luminaires.
When the lighting circuit load exceeds the rating of the photocell
contacts, a contactor must be used in conjunction with the photo-
cell.
Some luminaires designed for outside use offer an attached
photocell as an option for controlling that luminaire only. Photo-
cells are normally used to control exterior lighting by turning the
luminaires on at dusk and off at dawn. Common practice is to
mount the photocell on the north side of the building. For obvious
reasons, photocells should not be used in extremely dirty environ-
ments.
Timers
A lighting timer is a device that turns luminaires on or off at preset
times. Timers can be simple electro-mechanical devices with manual
stops that provide on–off switching, or sophisticated devices
programmed for sunrise and sunset times throughout the year. They

can be built into the program of a building management system so
that the lights come on at the beginning of the workday, and go
off at quitting time. There is a timer available to provide any
desired schedule for any facility. The only limiting factor in provid-
ing timer control is economics.
Occupancy sensors
Occupancy sensors are devices used to turn on lights when people
are in the space, and to turn them off when the space is vacant.
They are widely used in office spaces to conserve energy, and in
sensitive areas for security.
Three types of occupancy sensors are available: passive infrared,
or PIR, ultrasonic, and dual technology, which is a combination of
the two. All of the sensors contain timers that delay the action of
the switch for a preset time.
The PIR sensor detects the difference in infrared energy between
a human body and the surrounding space. When sufficient infrared
energy is detected, it closes a set of normally open contacts to turn
on the lights. The PIR sensor controls an area within its line of
sight, and within its coverage zone. False ‘ON’ can occur when
someone passes a doorway within sight of the sensor, and a false
‘OFF’ can occur if the room occupant is obscured by a piece of
furniture.
PIR sensors are best suited for:
1. enclosed open offices;
2. warehouses;
3. hallways;
4. areas with high air flow;
5. high ceiling areas.
They are poorly suited for:
1. restrooms;
2. storage areas with shelving;
3. offices with partitions.
The ultrasonic sensor uses the Doppler principle to sense motion
within the space: it bounces ultrasonic sound waves off objects in
the space, and measures the time that it takes the waves to return.
Movement by a person in the space disrupts the return time, and
the sensor reacts by closing a set of contacts. False ‘ON’ can occur
if there is high air flow within the space. False ‘OFF’ can occur if
the occupant of the space is inactive for longer than the delay
period.

Ultrasonic sensors work best in:
1. open plan office spaces;
2. conference rooms;
3. restrooms;
4. large areas.
They work poorly in:
1. spaces with high air flow;
2. spaces with high ceilings;
3. unenclosed areas.
The dual technology sensor utilizes both PIR and ultrasonic sensing,
and will not react unless both sensors detect occupancy, or the lack
thereof. This eliminates false ‘ON’ and false ‘OFF’ in most instances.
Dual technology sensors perform best in:
1. classrooms;
2. office spaces with partitions;
3. areas with high ceilings;
4. large open areas.
The only drawback to dual technology sensors is their relatively
high cost.
Occupancy sensors range in size from those which replace toggle
switches for single office applications, to those which are designed
to cover warehouses.
Light-sensitive controls
Light-sensitive controls are sensors that measure the ambient
daylight in a space, and then control the artificial lighting to
maintain a preset lighting level. These sensors contain an internal
photo conductive cell that measures light levels, and after a preset
delay, they either cut off luminaires, or dim them to a preset level.
These controls have been used with limited success, largely in areas
of the country that have minimal cloud cover. Obviously, the timing
of cloud passage cannot be predicted, so the setting of the delay
can present problems in areas with a high incidence of cloud cover.
These sensors contain internal switches for on–off control, and
electronic circuitry for electronic ballast control.
Example
Now that we’re all experts in powering and controlling lighting
systems, let’s take another look an Bullmoose Inc.’s office and

conference room addition, and see how we would make the system
work. The maintenance supervisor for Bullmoose has told us that
the voltage available in the building is 208Y120 V, three phase, and
the nearest panelboard to our area is several hundred feet away.
Instead of pulling all of our lighting circuits for that distance, it
makes more sense to install a small new 208Y120 V panelboard in
our area, and only pull one feeder circuit from the existing panel-
board. We know that there will be other circuits needed in the area
for receptacles, equipment, etc., so the cost of the new panelboard
is justified. We will flush mount the new panelboard in the office
space, out of sight from visitors. Now let’s wire up the lighting.
Let’s look at the office first. We can see from Figure 3.5 that we
have chosen six direct/indirect luminaires, each with three 32 W
lamps, for a total load of 576 W, assuming no reduction for our
electronic ballasts. At 120 V, our amp load is 576/120, or about
5 A. This is well within the capacity of one 20 A circuit, which you
will remember, is good for 16 A. This is also within the capacity of
a single 20 A switch, so we could control all the lights in the office
with one switch. For just a little extra money, we can put in another
switch, and allow control of the lighting level with the switching
scheme shown in Figure 4.6. Let’s do that. That will give the office
workers some control over the brightness in their room.
Standard practice is to put the switch on the lock side of the
door, so that a person entering the room may reach in and turn on
the lights without searching for the switch. We will assign one
circuit to the office lighting by itself, even though we have spare
capacity, so if the circuit breaker serving the office is tripped off,
only the office area will be affected.
Now what happens when everybody in the office goes to lunch
for an hour? Do you think that one of the workers will remember
to turn the lights off to save energy? Don’t count on it. With just
a little more expense, we can install an occupancy sensor to do the
job every time. We will need a dual technology sensor, since the
office has partitions in it, and the sensor will work best if it is
mounted in the ceiling in the center of the room so that it can ‘see’
into all the cubicles. The sensor should be wired ahead of, and in
series with the wall switches, so that it is only active when a switch
is in the ‘on’ position.
That done, let’s have a look at the conference room, which will
be a bit trickier. In reviewing the requirements for that room we
see that we will need full light over the conference table and
credenza when meetings are taking place, but only minimal light
there when a presentation is in progress. Our accent light for the
easel should be on full when a presenter is showing charts, but off

when a video presentation is in progress. Our accent lighting for
the art features, such as the portraits and the bust of the
Commodore should be on full for meetings, but subdued for presen-
tations. Upon closer examination, several scenes begin to arise from
these requirements.
Our architect has told us that Bullmoose Inc. doesn’t mind spend-
ing a little money on the conference room lighting, so we will use
a small computerized dimming system that has the capacity for, say,
four scenes. We will start with each of our lighting functions
separately circuited, each adjustable from a slider switch. The
conference table and credenza fluorescent ballasts will require a low
voltage signal, and the MR16 accent lights will be dimmed directly
from line voltage. The load for the 3–3 lamp conference table
luminaires will be 3 ⫻ 3 ⫻ 32 W, or 288 W. The credenza lighting
and east wall load will be 5 ⫻ 42 W, or 210 W. The accent
luminaires all use 75 W MR16 lamps, so the easel light load will
be 75 W, and the artwork lighting will be 4 ⫻ 75 W, or 300 W.
Obviously, none of these loads, or even all of these loads combined,
will exceed the 2000 W limit of one circuit. So instead of using four
power circuits for the conference room, we will use only two
circuits, one for the fluorescent dimmers, and one for the MR16
dimmers.
Now, would there be any benefit to using occupancy sensors for
the conference room? Probably not, because the same company
ferret who is assigned to make sure that the coffee and pastries
arrive on time, will also be responsible for turning the lights on and
off.
That takes care of circuiting the office and conference room.
What about the hallway – how will we handle the switching for
that, since the hallway can be entered from either end? This is
where we use three-way switching, as shown in Figure 4.5. We will
use one circuit for the hallway, and we have two luminaires with
two 40 W lamps each, or a total of 160 W.
Now what about power for the battery chargers for the
emergency and exit lighting? We will want to put those on their
own circuit, and label the circuit ‘EMERGENCY LIGHTS – DO
NOT TURN OFF’ by placing a sticker inside the panelboard beside
the circuit breaker serving this load. Each charger requires about
50 W, and we have a total of five chargers, so the load is 250 W.
Now let’s take a look at the loads that we have assigned to circuit
breakers:
• 720 W office lighting
• 288 W + 210 W = 498 W conference room fluorescent lighting

• 75 W + 300 W = 375 W conference room MR16 accent light-
ing
• 160 W hallway lighting
• 250 W emergency lighting battery chargers
Let’s use the panel schedule shown in Figure 4.2 to assign these
loads. If we put the 720 W office lighting load on circuit 1, which
is on bus A, we find that if we use circuit 2, also bus A, we will
have a heavy imbalance on bus A. So we will skip circuit 2, and
assign the conference room fluorescent lighting to circuit 3, which
is on bus B. We can assign the hallway lighting to circuit 4, also
on bus B, and have a total of 754 W on bus B. We assign the 375 W
conference room MR16 accent lighting load to circuit 5, on bus C,
and the 250 W emergency battery charger load to circuit 6, which
gives us a total load of 625 W load on bus C. This is not an ideal
balance of loads, but it is as close as we can get with the loads that
we have. This arrangement is shown in Figure 4.7. You will also
see in Figure 4.7 that the panel schedule has space to define the
circuit breaker and the circuit serving each load. As planned, we
will use single pole circuit breakers and no. 12 AWG wire run in
0.5 in. conduit.
Figure 4.7. Bullmoose office addition panel schedule.

We’ve now put together a luminaire layout, a luminaire sched-
ule, and a panel schedule for our space. What next? We’ll find out,
just as soon as we get these pesky exercises out of the way.
Exercises
1. What are the two voltages in the US of concern in lighting
design?
2. What size wire is normally used for lighting circuits?
3. What is the allowable amperage load on a 20 A molded case
circuit breaker?
4. What is the maximum number of circuit breaker spaces that
can be built into a panelboard?
5. How many amps of current would be drawn by 12–100 W
lamps connected to a 120 V circuit? A 277 V circuit?
6. What are the five components of a panelboard?
7. What are the functions of a circuit breaker in a lighting circuit?
8. What is meant by ‘balancing the load’ in a three-phase panel-
board?
9. What percent of fluorescent lamp wattage do most magnetic
ballasts consume as power loss?
10. What does the ‘T’ in the wiring designation THWN mean? The
‘W’?
11. What does ‘EMT’ mean when referring to conduit?
12. Can a single ballast fluorescent luminaire be double switched?
Why?
13. When an incandescent lamp is dimmed, does its color temper-
ature increase or decrease? Why?
14. What is a ‘scene’ as applied to computerized fluorescent
dimming?
15. What are the two methods for holding lighting contactors
closed?
16. What is the most common use for the photocell?
17. How many types of occupancy sensors are there? What are
they?
18. What type of occupancy sensor would you use in a school class-
room?
19. Would you use light-sensitive control of ambient lighting in an
area with a high incidence of cloud cover? Why?

OK, we have created a design for the Bullmoose, Inc. office
addition using catalogued lamps and luminaires, and we have
selected controls and circuits to make it work. Where do we go
from here?
Now we have to pull all of these elements together, and create a
set of contract documents that an electrical contractor can use to
bid on, and then use to build the system. The designer’s part of the
contract documents usually consists of a set of drawings, which
describe the system graphically, and the technical specifications,
which describe the components that the designer wants the contrac-
tor to use. Terms of contract, bidding procedures, etc., are usually
prepared by the lead professional, which in our case is the archi-
tect.
The contractor will first use these documents to prepare a bid for
constructing the project. His bid will include his cost for the compo-
nents shown on the drawings, plus his cost for labor to construct
the project, plus any overhead and materials markup that he
chooses to include. If the contractor is the successful bidder, he will
then use the documents to build the system.
If you as a designer have left a required component off of the
plans, or out of the specifications, it’s a sure bet that the contrac-
tor will find the oversight. The same holds true for components that
are sized incorrectly, and for designs that fail to meet the applica-
ble codes. During construction, the contractor will request a change
order to correct the deficiencies. Change orders invariably mean an
increase in contract price, and they tend to make owners and archi-
tects very unhappy – even to the point of requiring the delinquent
designer to pay for the changes out of his own pocket. You can
see, then, how imperative it is for contract documents to be
complete and accurate.
5 The contract documents

Figure
5.1.
Bullmoose
plan
sheet
start.

The project plans
So far, we’ve been pretty concise with our Bullmoose, Inc. design:
life safety codes have been met; luminaires have been selected to
meet our design requirements; and circuiting has all been well
within NEC requirements. So let’s put our luminaire schedule and
panel schedule on a single sheet to begin our plan set. This is shown
in Figure 5.1.
In order to show graphically what we intend the contractor to
do, we need to develop a legend of symbols that have specific
meaning on this drawing set. Standardized drawing symbols are
published in many architectural reference books, such as Archi-
tectural Graphic Standards published by John Wiley and Sons,
and other texts, all available from the IES publications division.
Many computerized drawing programs also contain libraries of
standard symbols. For our project, we will use the legend shown
in Figure 5.2
Now we need to show the wiring on the plan view, and identify
all the luminaires. This is shown in Figure 5.3.
All the wiring is identified in the panel schedule, with the excep-
tion of the extra conductor needed in the run between the two
The contract documents 113
Figure 5.2. Legend for Bullmoose office addition plan.

Figure
5.3.
Wiring
for
Bullmoose
office
addition
plan.

hallway three-way switches, which, if you recall from Figure 4.3, runs
from switch to switch. We will indicate this extra conductor by hatch-
ing the switch leg of the hallway lighting, as shown in Figure 5.3.
The circuit breaker in the existing building panelboard, the feeder
run from that panelboard to our new panelboard A, and new panel-
board A should be provided by the electrical contractor, if he is
different from the lighting contractor.
All the components and wiring are identified now, so our plans
are almost complete. All we need to add are some clarifying notes
and details to make sure that our intent is understood by the
contractor. We need to make sure that the contractor installs the
system in compliance with all applicable codes, so we’ll make this
note 1. Wiring is usually included in the electrical (rather than the
lighting) specifications, but it’s a good idea to specify the lighting
wiring on the lighting plans as well. This will be note 2. We want
to clarify responsibility for the circuit breaker in the existing build-
ing panel, the feeder to the new panel, and the new panel itself, so
we will make this note 3. The note will indicate that the electrical
contractor is to coordinate with the owner to identify the existing
panel from which our new panel will be fed. Note 3 will also make
reference to the electrical specification section which covers circuit
breakers and panelboards. Note 4 will require that the contractor
provide the exact luminaires that we show in the luminaire sched-
ule. This is necessary, because this is where a lot of lighting designs
go awry: most contractors have long-standing relationships with
suppliers who only carry specific brands of equipment. If our
contractor buys from a supplier who does not carry the luminaires
that we have specified, he will want to substitute luminaires that
his supplier does carry. The contractor is not aware of the design
criteria, and he may ask to substitute a luminaire that is unsuitable
for the job. Since the contractor’s bid is final, it is incumbent upon
the designer to make sure, before the bids, that he has the oppor-
tunity to accept or reject a contractor’s request for substitutions. In
our case, since we have worked closely with only one manufac-
turer’s representative and products, it is safer to not allow any
substitutions. A substitution clause will be included in note 4.
(A note on substitutions is appropriate here. If your project is
funded by public money, such as schools or government buildings,
it is mandated by law in most locations that you allow at least three
manufacturer’s products to be bid, in order to obtain the best
competitive price. If the project is privately funded, as is the case
with our Bullmoose, Inc. project, the designer may require that the
project be built as shown on the plans and specifications, with no
substitutions.)

Note 5 is a general CYA (Cover Your A—-) note to prevent
change order requests for things like trim, luminaire clips, lenses,
etc., which the contractor should have known to include in his bid.
The completed notes are shown in Figure 5.4.
We will add the notes to the drawing. Now what about details?
About the only thing in our design which isn’t standard construc-
tion practice is the double switching of the office luminaires, so
we’ll add the detail shown in Figure 4.6, and that will complete the
plans. Figure 5.5 shows the completed plan.
Now we will tackle the written part of the contract documents,
which will completely define the conditions, components and instal-
lation methods that are required for our project.
Project specifications
The Construction Specifications Institute (CSI) has established a 17
division specifications standard that encompasses all of the work to
be accomplished in a construction project. Within these divisions are
separate sections that contain the specifications for work within the
specific disciplines. Division 16000 is reserved for electrical work of
all types. Section 16400 pertains to interior electrical systems,
section 16500 covers lighting systems, and Section 16510 is for
interior lighting systems, and is of particular interest to us. Each
specification section is further broken down into three parts: Part 1
is the general conditions, which lists reference standards, special
project requirements, project scope, and submittals required of the
contractor; Part 2 is the products section, which lists the specific
Figure 5.4. Notes for Bullmoose office addition plan.
1.

Figure
5.5.
Bullmoose
Office
addition
completed
plan.

standards that the project components must meet; and Part 3 is the
execution section, which spells out how the contractor is to install
the components. What follows is a Section 16510 specification for
our Bullmoose, Inc. project, with explanatory notes in italics.
SECTION 16510 – INTERIOR LIGHTING
Part 1. General
1.1. References
The publications listed below form a part of this specification to
the extent referenced. The publications are referred to in the text
by the basic designation only.
AMERICAN NATIONAL STANDARDS INSTITUTE (ANSI)
ANSI C82.1 (1992) Ballasts for Fluorescent Lamps
ANSI C82.2 (1989) Fluorescent Lamp Ballasts – Methods of
Measurement
ANSI C82.11 (1993) High-frequency Fluorescent Lamp Ballasts
AMERICAN SOCIETY FOR TESTING AND MATERIALS (ASTM)
ASTM A 641 (1992) Zinc-coated (galvanized) Carbon Steel Wire
ILLUMINATING ENGINEERING SOCIETY OF NORTH AMERICA (IES)
LHBK (2000) Lighting Handbook, Ninth Edition
NATIONAL FIRE PROTECTION ASSOCIATION (NFPA)
NFPA 70 (1999) National Electric Code
NFPA 101 (1994) Code for Safety to Life from Fire in Build-
ings and Structures
UNDERWRITERS LABORATORIES INC. (UL)
UL 924 (1995) Emergency Lighting and Power Equipment
UL 935 (1995) Fluorescent Lamp Ballasts
UL 1570 (1995) Fluorescent Lighting Fixtures
UL 1571 (1996) Incandescent Lighting Fixtures
All of the organizations listed above have put in a lot of effort and
expense into developing exacting specifications for components that
we have used in our design. By referencing these published
standards, we incorporate the standards into our specifications.
1.2. Related requirements
Section 16050 ‘Basic Electrical Materials and Methods’ applies to
this section, with the modifications and additions specified herein.

Materials not considered to be lighting equipment are specified in
Section 16402 ‘Interior Distribution System’.
The project electrical engineer normally prepares all division
16000 specifications, and references are made between sections,
rather than rewriting the same clauses in every section. We will
approach this section from the standpoint of the lighting designer
who will integrate Section 16510 into the rest of the division 16000
sections prepared by others.
1.2.1. Work Included
The work included under these specifications consists of furnishing
and installing all luminaires, controllers, wiring, conduit, and other
necessary appurtenances to provide a fully functional lighting system
as shown on the plans. The contractor shall provide all materials,
labor, tools, and equipment necessary to complete the project.
1.3. Definitions
1.3.1. Average life (lamps)
The time after which 50% will have failed, and 50% will have
survived under normal conditions.
1.3.2. Total Harmonic Distortion (THD)
The root mean square (RMS) of all the harmonic components
divided by the total fundamental current.
The power supplies used in fluorescent electronic ballasts gener-
ate harmonics that can feed back into the electrical system and
cause problems with sensitive electrical equipment. It is necessary
for the lighting designer to specify a maximum allowable harmonic
distortion for the ballasts.
1.4. Submittals
Other sections of the specification require the contractor to submit
to the designer manufacturer’s catalog sheets of the materials he
proposes to use on the project. The designer then reviews the
submittals, and either approves or rejects them. The contractor
cannot install an item until he has an approved submittal for the
item signed by the designer.
Submit the following in accordance with the section entitled
‘Submittal Procedures’. Data, drawings, and reports shall employ
the terminology, classifications, and/or methods prescribed by the
IES LHBK, as applicable, for the lighting system specified.
1.4.1. Manufacturer’s catalog data
a. Fluorescent luminaires;
b. fluorescent electronic ballasts;

c. fluorescent lamps;
d. incandescent luminaires;
e. low voltage incandescent lamps;
f. dimmer system;
g. exit signs;
h. emergency lighting equipment;
i. occupancy sensors.
This is the data that the contractor has to submit for approval.
Switches, wire, panelboards, circuit breakers, and conduit are speci-
fied in Section 16402 by the electrical engineer. The lighting
designer should coordinate closely with the electrical engineer to
ensure that the components specified are compatible with the light-
ing system design
1.5. Electronic ballast warranty
Furnish the electronic ballast manufacturer’s warranty. The
warranty period shall not be less than 5 years from the date of
manufacture of the ballast. Luminaires, including ballast assembly,
shall be installed within 1 year after manufacture, leaving at least
4 years of the warranty in effect after installation.
Part 2. Products
2.1. Fluorescent luminaries
Luminaires shall comply with UL 1570. Fluorescent luminaires shall
have electronic ballasts.
2.1.1. Fluorescent lamp electronic ballasts
The electronic ballast shall, as a minimum, meet the following crite-
ria:
a. ballast shall comply with UL935, ANSI C82.11, and NFPA
70. Ballasts shall be designed for the number and wattage of
the lamps shown on the plans. Ballasts are to operate on
120 V, AC;
b. power factor shall be 0.95 minimum;
c. ballast shall operate at a frequency of 20 000 Hz (minimum);
d. ballast shall have light regulation of plus or minus 10%
lumen output with a plus or minus 10% input voltage regula-
tion. Ballast shall have a maximum of 10% flicker;
e. ballast shall be UL listed Class P with a sound rating of ‘A’;
f. ballast shall have circuit diagrams and lamp connections
displayed on the ballast enclosure. Ballasts shall operate
lamps in a parallel configuration that permits the operation
of the remaining lamps if one lamp fails;

g. ballasts shall operate in a rapid start mode;
h. ballasts shall have a full replacement warranty as specified in
paragraph 1.5;
i. ballasts shall have a total harmonic distortion (THD) of
15%.
As a general rule of thumb, the lower the THD percentage, the
larger the ballast power supply, and, as we remember from Chapter
2, the larger the current inrush when the lights are switched on. If
you have a large number of luminaires with very low THD ballasts
connected on a circuit, it is likely that the circuit breaker will trip
when you turn on the switch; 15% THD is about as low as we
need to go, except in special cases.
2.1.1.1. T-8 Electronic ballast
a. Ballasts shall have input wattage of 114 W maximum when
operating four F32T8 lamps.
2.1.1.2. T-8 Electronic dimming ballasts
a. Ballasts shall have the capability to continuously dim the
output of its connected lamps from full output to 10% of
full output. Dimming shall be accomplished by electronic
circuitry responding to a low voltage (24 V) signal from a
dimming system.
2.1.1.3. T5 Long twin tube ballasts
a. Ballasts shall have input wattage of 74 W maximum when
operating two CF40T5 lamps.
2.1.1.4. Compact fluorescent electronic dimming ballast
a. Ballasts shall be solid state, dimming type, capable of contin-
uously dimming the output of its connected lamps from full
output to 10% of full output. Dimming shall be accom-
plished by electronic circuitry responding to a low voltage
(24 V) signal from a dimming system.
2.1.2. Fluorescent Lamps
2.1.2.1. T-8 Lamps
T8 rapid start lamps shall be rated 32 W, 2800 initial lumens
minimum, CRI of 72 minimum, color temperature of 4100 K, and
an average rated life of 20 000 h.
2.1.2.2. T-5 Lamps
T5 long twin tube fluorescent lamps shall be rated 40 W, 3150
initial lumens minimum, CRI of 72 minimum, color temperature of
4100 K, and an average rated life of 20 000 h. Lamps shall be
22.6 in. maximum length, and shall have a 2G11 type base.

2.1.2.3. Compact fluorescent lamps
Compact fluorescent lamps shall be rated 26 W, 1800 initial lumens
minimum, CRII of 72 minimum, color temperature of 4100 K, and
an average rated life of 10 000 h. Lamps shall be double twin tube,
with four pin base for dimming.
2.2. Incandescent luminaires
1. Incandescent luminaires are to be provided complete with trans-
formers, and circuitry required for the operation of low voltage
MR-16 lamps. The luminaires are to provide tool-less lamp
adjustment in both the horizontal and vertical planes to allow
aiming of the lamp. All required trim, lenses, hangers, etc.,
required for complete installation are to be provided with the
luminaires.
2. MR-16 lamps are to be 75 W, with an average rated life of
4000 h.
a. Narrow spot lamps are to have a beam spread of 10°
maximum, with a center of beam candlepower rating of
10 000 candlepower. This lamp will be used to highlight the
bust of Commodore Bullmoose;
b. medium beam flood lamps are to have a beam spread of 24°
maximum, with a center of beam candlepower rating of 3100
candlepower. This lamp will be used to illuminate the presen-
tation easel;
c. flood lamps are to have a beam spread of 36° maximum,
with a center of beam candlepower rating of 1800 candle-
power. This lamp will be used to wall wash the portraits.
2.3. Dimming system
2.3.1. Construction
The dimming system shall be housed in a steel frame with hinged
faceplate. It shall be designed to fit in a standard five-gang
backbox.
2.3.2. Functionality
The dimming system shall provide the following features:
a. single control to turn off all lighting;
b. master raise/lower control to raise or lower the lighting levels
of all luminaires simultaneously;
c. channel raise/lower control to raise or lower the lighting level
of luminaires connected to the individual channels;
d. preset controls for saving preset scenes;
e. adjustable fade time for preset scenes. Fade time will be
adjustable from 0 to 45 seconds.

2.3.3. Capacities
The system shall be capable of dimming a minimum combined load
of 2000 W. It shall be capable of dimming fluorescent electronic
ballasts, compact fluorescent lamp ballasts, and low voltage incan-
descent loads. It shall provide a minimum of four separate dimming
channels, and have a minimum of four preset scenes involving all
channels. Each channel shall have capacity for:
a. 600 W of electronic ballast load;
b. 800 W of incandescent load.
2.4. Exit signs
Exit signs shall be self-powered LED type, conforming to UL924,
NFPA 70, and NFPA 101.
2.4.1. Self-powered LED exit signs (battery backup)
Sign shall be provided with automatic transfer switch, battery, and
automatic high/low trickle charger contained within the sign.
Battery shall be sealed electrolyte type, and shall require no mainte-
nance, including no additional water, for a period of not less than
5 years. The battery shall be capable of powering the sign for a
minimum of 90 minutes.
2.5. Emergency lighting equipment
Emergency lighting equipment shall conform to UL934, NFPA 70,
and NFPA 101.
2.5.1. Fluorescent emergency system
Shall be suitable for use with solid state ballasts. Each system shall
contain an automatic transfer switch, battery, and automatic
battery charger contained within an enclosure in a standard
luminaire. The system shall include a test switch, operable from
outside the fixture, and a pilot light, visible from outside the
fixture. Battery is to be sealed electrolyte type, with capacity to
provide power to one lamp at an output of 1100 lumens, for a
period of 90 minutes. The battery shall require no maintenance,
including no additional water, for a period of not less than 5
years.
2.6. Occupancy sensors
Occupancy sensors shall be UL listed. Sensor mounting type shall
be ceiling surface. Detector shall be combination passive
infrared/ultrasonic. Sensor shall have LED positive detection indica-
tor, adjustable delayed off – time range between 30 seconds and 15
minutes, and sensitivity adjustment. Input shall be rated for 120 V,
AC. Contacts shall be rated for 15 A minimum. Sensor shall have

‘fail – on’ function designed to keep the lights on if the sensor fails.
Sensor shall have a manual override switch.
2.7. Support hangers for luminaires in suspended ceilings
2.7.1. Wires
Wires shall conform to ASTM A 641, class 3 soft temper, 12 gauge,
zinc-coated finish.
Part 3. Execution
3.1. Installation
Set luminaires square, plumb, and level with ceiling and walls.
Luminaires shall be in alignment with adjacent luminaires, and
secure in accordance with manufacturer’s directions and approved
drawings. Installation shall meet the requirements of NFPA 70.
Contractor shall obtain approval of the exact mounting for
luminaires before commencing installation, and after coordinating
with the other trades involved.
Lighting and HVAC (heating, ventilating, and air conditioning)
diffusers compete for ceiling space in a grid ceiling. In this project,
it is important that our luminaires be placed where we have shown
them, and any conflicts should be worked out before the two
contractors begin work.
Recessed luminaires may be supported from suspended ceiling
system support tees when the ceiling system support wires are
provided at a minimum of four wires per luminaire, and located not
more than 6 in. from the corner of each luminaire. In areas having
seismic requirements, it will be necessary to provide an extra two
wires per luminaire. Provide support clips securely fastened to ceiling
grid members, one at each corner of the luminaire. For luminaires
smaller than the ceiling grid, provide a minimum of four wires per
luminaire, located at the corners of the grid in which the luminaire is
mounted. In our case, this would be the recessed downlights in the
conference room. Do not support luminaires by ceiling acoustical
panels. Where luminaires smaller than the ceiling grid are mounted in
the center of the acoustical panel, support the luminaire with at least
two 3/4 in. metal channels spanning, and secured to, the ceiling grid.
3.1.1. Exit signs and emergency lighting units
Wire exit signs and emergency lighting equipment on a separate
circuit breaker in the lighting panelboard. Place a sticker beside this
breaker which states ‘EMERGENCY LIGHTING – DO NOT
TURN OFF’, and provide lockout.

3.1.2. Occupancy sensor placement
Locate the sensors in accordance with the manufacturer’s recom-
mendations to maximize energy savings and to avoid nuisance
activation.
3.2. Field quality control
Upon completion of the installation, conduct an operating test to
show that all components of the lighting system operate in accor-
dance with this section.
And there we have it! We can send the contract documents to the
architect and send him our invoice. Our work here is done, masked
man. . . or is it?
When the project bids come in, the owner will probably suffer
what is commonly known as ‘price tag shock’. The cost for the
project is higher than he had expected. He will huddle with the
architect and the low bid contractor and try to come up with some
ways to cut costs. The first item on the chopping block will be –
you guessed it – the lighting system. The contractor will say that
he can cut a lot of money out of the job if he is allowed to substi-
tute generic luminaires for all that fancy stuff that you’ve specified.
It’s up to you to stand fast, and hold to your design. You have
selected the luminaires through a careful process, and the system
will function exactly as the architect has specified, at the lowest
energy cost possible. You can enlist the support of the architect on
this point. If your design is compromised, you can bet that, a year
from now, nobody will remember the few dollars that were saved
on the lighting, but they will curse the inferior system that they are
having to endure. Your reputation as a lighting designer and the
workers who occupy the space will both suffer if you allow the
substitution of inappropriate fixtures into your design.
Enough of the soap box – now let’s get on to those snappy
exercises that we all know and love.
Exercises
1. What are the two uses that a contractor has for the contract
documents?
2. What do the technical contract documents include?
3. Under what circumstances could the designer be required to pay
for part of the project? What part would the designer be asked
to pay for?
4. Why do we put a symbol legend on the drawings?

5. How do we identify wire and conduit sizes in our Bullmoose,
Inc. project?
6. If you are designing a government project, funded by public
money, how many manufacturers must you allow to bid on
your project?
7. If you are designing a project that is funded by private money,
how many manufacturers must you allow?
8. What is the purpose of the technical specifications?
9. How many divisions are there in a standard construction speci-
fication?
10. How many parts are there in each technical specification
section?
11. Why do we list reference publications and materials standards
in Part 1 of the technical specifications?
12. Why do we require the contractor to submit manufacturer’s
data on the products that he intends to use on our project?
13. What does the designer do with the submittals?
14. Why don’t we specify 0% THD in our ballast specifications,
since harmonics are undesirable in an electrical system?
15. Why do we require tool-less adjustment in our adjustable
luminaires?
16. Why do we need a ‘fail – on’ function for an occupancy sensor?
17. Why does the lighting contractor need to coordinate with the
HVAC contractor before starting work in the ceiling?
18. Why do we require an operational test after the installation is
complete?

The problem
Back in the 1970s, the 1980s, and even into the 1990s, open plan office
spaces were all the rage, and the lighting design for these spaces was
done largely by rule of thumb. The luminaire of choice was the 2 ft ⫻
4 ft (0.6 m ⫻ 1.2 m) recessed fluorescent troffer with four F40T12/735
lamps, magnetic ballasts, and flat acrylic diffusers. These luminaires
were laid out at 8 ft (2.4 m) on center throughout the space.
Given these parameters, the luminaire manufacturers could only
compete on one basis – price. Manufacturers scrambled to cut
manufacturing costs to the bone, and in doing so, the performance
of the luminaires suffered. For the most part, this didn’t matter
much, because the spaces were so over-lit that even with a light loss
factor (LLF) of 0.40, the design still produced plenty of light (and
glare) for the workers in the spaces.
On the manufacturing side, the reflector panels in the luminaires
were designed to minimize manufacturing costs, rather than to
improve luminaire performance. Ballasts were built as cheaply as
possible, at the expense of ballast factor. Even the acrylic diffusers
suffered, by becoming thinner – some as thin as 0.10 in. (2.5 mm)
– which reduced the prismatic diffusion pattern to randomly sized
‘lumps’ on the surface of the diffuser. All this served to give the
luminaire a very poor efficiency.
As energy prices continued to rise, this luminaire inefficiency put
an ever larger bite on the pocketbook of building owners, causing
them, for the first time, to notice the lighting. Then, in 1992, along
came EPACT 92, which outlawed the manufacture of cheap
F40T12 lamps, and suddenly, building maintenance engineers
couldn’t find replacements for burned out lamps.
Lamp manufacturers came up with an alternative that met the
requirements of EPACT 92, and which would operate on the
6 The second time around –
retrofitting

installed 40 W magnetic ballasts. This was the F34T12 ‘Energy
Saver’ lamp, which was installed as the F40T12 lamps burned out.
As we said earlier in this book, there is no free lunch. Lower
wattage lamps in an already inefficient luminaire meant less light
output, and in general, poor lighting. To make matters worse, the
F34T12 lamps didn’t provide the expected energy savings, because
they operated inefficiently on the old 40 W ballasts. Many millions
of square feet of existing office, hospital, and manufacturing space
are presently operating under these conditions, using either aging
F40T12 lamps, or the F34T12 lamps.
The solution
One solution to this problem would be to replace the old luminaires
with new, efficient luminaires that use F32T8 lamps, and the much
more efficient electronic ballasts. This is a very expensive option,
and one that has a payback time (the time required for the energy
savings to offset the installation costs) unacceptable to most build-
ing owners. A much more attractive option is to retrofit the exist-
ing luminaires to improve their efficiency. This means:
• improving the optics of the luminaires
• upgrading the ballasts of the luminaires
• installing F32T8 lamps and lampholders.
This will allow the existing luminaire housings and wiring to
remain in place, while greatly improving luminaire performance and
efficiency.
Just how do we go about retrofitting a luminaire? Let’s take a
look.
Improving luminaire optics
When the luminaires were built, the sheet metal that forms the
housing of the luminaire was shaped to contain the ballast, and to
mount the lamps, without much regard for optic performance. The
resulting ‘box’ shape of the housing allowed light from the lamps
to scatter within the housing, and most of the light from the upper
half of the lamp was lost.
Reflectors are now being manufactured that redirect that light
downward into the usable zone. These reflectors are available to
accommodate the standard two, three, and four lamp configura-
tions of the 2 ft ⫻ 4 ft (0.6 m ⫻ 1.2 m) troffer, and are designed
to fit into existing housings with a minimum of extra hardware.

Typically, the reflectors are manufactured from material that has a
90–95% reflectivity, and that is formed to direct all available light
out of the luminaire. When in place, reflectors alone can boost the
efficiency of the older luminaires by 20–30%, with no increase in
energy usage. It is common retrofit practice to replace four F40T12
lamps and two magnetic ballasts with two F32T8 lamps, one
electronic ballast, and reflectors. This saves 100 W per luminaire in
lamp energy, and about 30 W per luminaire in ballast loss.
The acrylic diffusers in the older troffers were often of poor
quality, and as a result, scattered some of the usable light. Dirt
accumulation and aging has reduced the transmissivity of the mater-
ial, resulting in additional light loss. Some of the earlier diffusers
were made of polycarbonate, which, as we saw in Chapter 2,
yellows with age, and that further reduces the light output of the
luminaire. Modern prismatic acrylic diffusers are manufactured
with precisely formed prisms that serve to direct light downward
as usable light. The diffuser is normally changed during the retro-
fit process. Now, what about the rest of the luminaire?
Upgrading the ballast
This is a simple one. We simply discard the old, inefficient magnetic
ballasts and replace them with a new electronic ballast, don’t we?
That’s exactly what needs to be done, but it may not be quite
that easy. The old ballast could contain PCBs (polychlorinated
biphenyls), which we can’t just throw in the local landfill, because
PCBs have been determined to be hazardous. We first have to
contact the ballast manufacturer and determine that the old ballasts
do not contain PCBs. Then we discard them. If they do, they must
be disposed of in a manner prescribed by the US Environmental
Protection Agency (EPA). This costs a little more, but either way,
we get rid of the inefficient magnetic ballasts and replace them with
an electronic ballast. This gives us a big jump in efficiency since the
magnetic ballasts can only operate two lamps – and therefore two
ballasts are required for a four-lamp luminaire – which produces
double the ballast loss. Now, what about upgrading the lamps?
Upgrading the lamps
Naturally, we want to go with the more efficient F32T8 lamps, but
let’s go one step further, and use 4100 K lamps, instead of the
3500 K ‘cool white’ F40T12 lamps that we’re taking out. This will
give us a little whiter light, and also the perceived impression of
more light. This will help when we replace four F40T12 lamps in
The second time around – retrofitting 129

an inefficient luminaire with two F32T8 lamps in our improved
luminaire. The actual footcandle level at the desktop may be the
same, plus or minus a few footcandles, but the space will seem
much better lighted. If you remember the opening paragraph of this
book, psychology is an important part of lighting, and it will come
into play here. As a bonus, we have reduced the amount of air
conditioning required to remove the waste heat from the inefficient
luminaires.
It’s easy to see that we have reduced the energy consumption of
the system. We have replaced four 40 W lamps with two 32 W
lamps, and we have improved the ballast factor from around 0.6
to at least 0.8. Plus, we have reduced the air conditioning load. But
that’s not all. The maintenance costs for the retrofitted luminaires
will be reduced by at least half, since we now have only two lamps
and one ballast per luminaire to maintain. All of this contributes
toward producing a low payback time, which makes retrofitting
economically attractive to building owners. In addition, if you
multiply all this by the millions of luminaires currently in service,
you can see how retrofitting aging luminaires can greatly improve
the national energy picture.
Let’s take a concrete example, and see how it looks.
Figure 6.1. Office retrofit layout.

Let’s say that we’ve been called in to survey a 80 ft ⫻ 80 ft open
plan office space which is lighted by the typical four-lamp F40T12
luminaires, and we’ve been asked to show the payback for retro-
fitting the luminaires. The layout is shown in Figure 6.1.
We see that the luminaires are laid out on the typical 8 ft ⫻ 8 ft
pattern, and that there are 100 luminaires. We can now compute
the yearly energy savings for the system by calculating a ‘before and
The second time around – retrofitting 131
Figure 6.2. ENLIGHTEN retrofit economic analysis (courtesy of United Energy Associates Inc.).

after’ scenario, throw in the expected air conditioning savings,
estimate the cost of retrofit, both labor and materials, estimate
maintenance costs, run an economics analysis, and come up with
an estimated payback time for the owner. If you do this by hand,
it will probably take a day or two. A much easier approach is to
use a packaged computer program to do the calculations for us.
The program that we will use for this example is a proprietary
program developed by United Energy Associates, Inc., of Winter
Haven, Florida. The program is called ENLIGHTEN, and is avail-
able for purchase from United Energy Associates. Figure 6.2 shows
the results of the ENLIGHTEN run for our example.
From Figure 6.2 it is seen that the capital recovery (or payback)
time is 12.18 months, or a little over a year. After that, the savings
to the building owner will be $4802.00 per year. This would repre-
sent a good value to the building owner, who would normally
consider a payback time of under 3 years a sound investment.
For you environmentalists, you can also see that by reducing the
energy consumption of the building, the amount of pollutants
released into the air by generating plants has been reduced. In our
case, the release of about 225 000 pounds per year of carbon
dioxide, sulfur dioxide, and nitrous oxide has been avoided.
That’s the retrofitting story. It’s one of those rare cases where
everybody wins. You as a designer should consider retrofitting as
another valuable tool in your arsenal.
And that’s about it for this book. Although I know you’ve grown
to love them, you won’t have any exercises to do for this chapter.
Go forth and design!

Accent Lighting: Directional lighting to emphasize a particular
object or to draw attention to a part of the field of view.
Absorption: The dissipation of light within a surface or medium.
Accommodation: The process by which the eye changes focus from
one distance to another.
Adaptation: The process by which the visual system becomes accus-
tomed to more or less light than it was exposed to during an
immediately preceding period. It results in a change in the sensi-
tivity of the eye to light.
Air Fitting (air bonnet, air hood, air saddle, air box): A fitting that
is mounted to an air handling luminaire and connects to the
primary air duct by flexible ducting. It normally contains one or
two volume controls.
Alternating Current (AC): Flow of electricity that cycles or alter-
nates direction many times per second. The number of cycles per
second is referred to as frequency. Most common frequency used
in the US is 60 Hertz (Hz; cycles per second) in Europe, 50 Hz is
the standard.
Ambient Lighting: General lighting, of the space (as opposed to
task lighting or the lighting of the object one is looking at). It
can be produced by direct lighting from recessed, surface or
stem-mounted luminaires, or by indirect lighting that is wall or
stem mounted, or by luminaires built into furniture or free
standing.
Amperes (amps or A): The unit of measurement of electric current.
Baffle: An opaque or translucent element that serves to shield a
light source from direct view at certain angles, or serves to absorb
unwanted light.
Glossary

Ballast: An auxiliary device used with fluorescent and HID lamps
to provide the necessary starting voltage and to limit the current
during operation.
‘Batwing’ Distribution: Candlepower distribution that serves to
reduce glare and veil reflections by having its maximum output in
the 30–60° zone from the vertical and with a candlepower at nadir
(0°) being 65% or less than maximum candlepower. The shape is
similar to a bat’s wing. In fluorescent luminaires the batwing distri-
bution is generally found only in the plane perpendicular to the
lamps.
Beam Spread: The angle enclosed by candlepower distribution curve
at the two lines that intersect the points where the candlepower is
equal to 10% of its maximum.
Branch Circuit: An electrical circuit running from a service panel
having its own overload protection device.
Brightness (Luminance): The degree of apparent lightness of a
surface; its brilliancy; concentration of candlepower. Brightness is
produced by either a self-luminous object, by light energy trans-
mitted through objects or by reflection. Unit of measurement of
brightness is the footlambert (fl).
Candela: The unit of measurement of luminous intensity of a light
source in a given direction.
Candlepower: Luminous intensity expressed in candelas.
Candlepower Distribution Curve: A graphic presentation of the
distribution of light intensity in a given plane of a lamp or
luminaire. It is determined by photometric tests. The curve is gener-
ally polar, representing the variation of luminous intensity of a lamp
or luminaire in a plane through the light center.
Capacitor: An electric energy storage device that when built into or
wired to a ballast changes it from low to high power factor.
Cavity Ratio: A number indicating room cavity proportions calcu-
lated from length, width and height.
Ceiling Cavity Ratio: A numerical relationship of the vertical
distance between luminaire mounting height and ceiling height to
room width and length. It is used with the zonal cavity method of
calculating average illumination levels.
Circuit Breaker: Resettable safety device to prevent excess current
flow.

Class ‘P’ Ballast: Contains a thermal protective device that deacti-
vates the ballast when the case reaches a certain critical tempera-
ture. The device resets automatically when the case temperature
drops to a lower temperature.
Coefficient of Utilization (CU): A ratio representing the portion of
light emitted by a luminaire in any particular installation that
actually gets down to the work plane. The coefficient of utilization
thus indicates the combined efficiency of the luminaire, room
geometry and room finish reflectances.
Cold Cathode Lamp: An electric-discharge lamp whose mode of
operation is that of a glow discharge.
Color Rendering Index (CRI): Measure of the degree of color shift
objects undergo when illuminated by the light source as compared
with the color of those same objects when illuminated by a refer-
ence source of comparable color temperature.
Color Temperature: The absolute temperature of a black body
radiator having a chromaticity equal to that of the light source.
Cone Reflector: Parabolic reflector that directs light downward
thereby eliminating brightness at high angles.
Contrast: The difference in brightness (luminance) of an object and
its background.
Contrast Rendition Factor (CRF): The ratio of visual task contrast
with a given lighting environment to the contrast with sphere
illumination. Contrast measured under sphere illumination is
defined as 1.00.
Cool Beam Lamps: Incandescent reflector lamps that use a special
coating (dichronic interference filter) on the reflectorized portion of
the bulb to allow infrared heat to pass out the back while reflect-
ing only visible energy to the task, thereby providing a ‘cool beam’
of light.
Cut-off Luminaires: Outdoor luminaires that restrict all light output
to below 85° from vertical.
Cut-off Angle (of a luminaire): The angle from the vertical at which
a reflector, louver, or other shielding device cuts off direct visibility
of a light source. It is the complementary angle of the shielding
angle.
Dimming Ballast: Special fluorescent lamp ballast, which when used
with a dimmer control, permits varying light output.
Glossary 135

Direct Current (DC): Flow of electricity continuously in one direc-
tion from positive to negative.
Direct Glare: Glare resulting from high luminances or insufficiently
shielded light sources in the field of view. It usually is associated
with bright areas, such as luminaires, ceilings and windows that are
outside the visual task or region being viewed.
Discharge Lamp: A lamp in which light (or radiant energy near the
visible spectrum) is produced by the passage of an electric arc
through a vapor or a gas.
Discomfort Glare: Glare producing discomfort. It does not neces-
sarily interfere with visual performance or visibility.
Distribution Panel: Panelboard containing circuit breakers that
distribute power to branch circuits.
Efficacy: See Lamp Efficacy.
Efficiency: See Luminaire Efficiency.
Equivalent Sphere Illumination (ESI): The level of sphere illumina-
tion that would produce task visibility equivalent to that produced
by a specific lighting environment. Suppose a task at a given location
and direction of view within a specific lighting system has 100 fc of
illumination. Suppose this same task is now viewed under sphere
lighting and the sphere lighting level is adjusted so that the task
visibility is the same under the sphere lighting as it was under the
lighting system. Suppose the lighting level at the task from the sphere
lighting is 50 fc for equal visibility. Then the equivalent sphere illumi-
nation of the task under the lighting system would be 50 ESI fc.
‘ER’ (Elliptical Reflector): Lamp whose reflector focuses the light
about 2 ft (61 cm) ahead of the bulb, reducing light loss when used
in deep baffle downlights.
Extended Life Lamps: Incandescent lamps that have an average
rated life of 2500 or more hours and reduced light output compared
to standard general service lamps of the same wattage.
Floodlighting: A system designed for lighting a scene or object to
a luminance greater than its surroundings. It may be for utility,
advertising or decorative purposes.
Fluorescent Lamp: A low-pressure mercury electric-discharge lamp
in which a fluorescing coating (phosphor) transforms some of the
ultraviolet energy generated by the discharge into light.
Flux: Continuous flow of luminous energy.

Footcandle (fc): The unit of illuminance when the foot is taken as
the unit of length. It is the illuminance on a surface one square foot
in area on which there is a uniformly distributed flux of 1 lumen.
(Raw) Footcandles: Same as footcandles. This term is sometimes
used in order to differentiate between ordinary footcandles and ESI
footcandles. (Footcandles or Raw Footcandles refer only to the
quantity of illumination. ESI footcandles refer to task visibility by
considering both the quantity and quality of illumination.)
Foot Lambert: A unit of luminance of a perfectly diffusing surface
emitting or reflecting light at the rate of 1 lumen per square foot.
Fuse: Replaceable safety device to prevent excess current flow.
General Lighting: See Ambient Lighting.
General Service Lamps: ‘A’ or ‘PS’ incandescent lamps.
Glare: The sensation produced by luminance within the visual field
that is sufficiently greater than the luminance to which the eyes are
adapted to cause annoyance, discomfort, or loss in visual perfor-
mance and visibility.
Greenfield: Flexible metallic tubing for the protective enclosure of
electric wires.
Grounding: Connection of electric components to earth for safety.
Group Relamping: Relamping of a group of luminaires at one time
to reduce relamping labor costs.
Heat Extraction: The process of removing heat from a luminaire
by passing return air through the lamp cavity.
High Intensity Discharge (HID) Lamp: A discharge lamp in which
the light-producing arc is stabilized by wall temperature, and the
arc tube has a bulb wall loading in excess of 3 W per square
centimeter. HID lamps include groups of lamps known as mercury,
metal halide, and high pressure sodium.
High Output Fluorescent Lamp: Operates at 800 or more
milliamperes (mA) for higher light output than standard fluorescent
lamp (430 mA).
High Pressure Sodium (HPS) Lamp: High intensity discharge (HID)
lamp in which light is produced by radiation from sodium vapor.
Includes clear and diffuse-coated lamps.
Incandescent Lamp: A lamp in which light is produced by a
filament heated to incandescence by an electric current.
Glossary 137

Instant Start Fluorescent Lamp: A fluorescent lamp designed for
starting by a high voltage without preheating of the electrodes.
Inverse Square Law: The law stating that the illuminance at a point
on a surface varies directly with the intensity of a point source, and
inversely as the square of the distance between the source and the
point.
Isolux Chart: A series of lines plotted on any appropriate set of
coordinates, each line connecting all the points on a surface having
the same illumination.
Joule Heating: Heating which occurs when an electric current is
passed through a conductor having electrical resistance. The
amount of heat generated is directly proportional to the resistance,
and to the square of the current (Wjoule = I squared ⫻ R).
Junction Box: A metal box in which circuit wiring is spliced. It may
also be used for mounting luminaires, switches or receptacles.
Kilowatt-hour (kWh): Unit of electrical energy, or power consumed
over a period of time. kWh = watts/l000 ⫻ hours used.
Lamp: An artificial source of light (also a portable luminaire
equipped with a cord and plug).
Lamp Efficacy: The ratio of lumens produced by a lamp to the
watts consumed, expressed as lumens per watt (LPW).
Lamp Lumen Depreciation (LLD): Multiplier factor in illumination
calculations for reduction in the light output of a lamp over a
period of time.
Light: Radiant energy that is capable of exciting the retina and
producing a visual sensation. The visible portion of the electro-
magnetic spectrum extends from about 380–770 nm.
Light Loss Factor (LLF): A factor used in calculating the level of
illumination that takes into account such factors as dirt accumula-
tion on luminaire and room surfaces, lamp depreciation, mainte-
nance procedures and atmosphere conditions. See Maintenance
Factor.
Light Output: Amount of light produced by a light source such as
a lamp. The unit most commonly used to measure light output is
the lumen.
Lens: Used in luminaires to redirect light into useful zones.
Local Lighting: Lighting designed to provide illuminance over a

relatively small area or confined space without providing any signif-
icant general surrounding lighting.
Louver: A series of baffles used to shield a source from view at
certain angles or to absorb unwanted light. The baffles are usually
arranged in a geometric pattern.
Long Life Lamps: See Extended Life Lamps.
Low Pressure Sodium Lamp: A discharge lamp in which light is
produced by radiation of sodium vapor at low pressure producing
a single wavelength of visible energy, i.e. yellow.
Low Voltage Lamps: Incandescent lamps that operate at 6–12 V.
Lumen: The unit of luminous flux. It is the luminous flux emitted
within a unit solid angle (1 steradian) by a point source having a
uniform luminous intensity of 1 candela.
Luminaire: A complete lighting unit consisting of a lamp or lamps
together with the parts designed to distribute the light, to position
and protect the lamps and to connect the lamps to the power
supply.
Luminaire Dirt Depreciation (LDD): The multiplier to be used in
illuminance calculations to relate the initial illuminance provided by
clean, new luminaires to the reduced illuminance that they will
provide due to dirt collection on the luminaires at the time at which
it is anticipated that cleaning procedures will be instituted.
Luminaire Efficiency: The ratio of luminous flux (lumens) emitted
by a luminaire to that emitted by the lamp or lamps used therein.
Luminance: See Brightness. The amount of light reflected or trans-
mitted by an object.
Lux: The metric unit of illuminance. One lux is one lumen per
square meter (lm/m2).
Maintenance Factor (MF): A factor used in calculating illuminance
after a given period of time and under given conditions. It takes
into account temperature and voltage variations, dirt accumulation
on luminaire and room surfaces, lamp depreciation, maintenance
procedures and atmosphere conditions.
Matte Surface: A non-glossy dull surface, as opposed to a shiny
(specular) surface. Light reflected from a matte surface is diffuse.
Mercury Lamp: A high intensity discharge (HID) lamp in which
the major portion of the light is produced by radiation from
Glossary 139

mercury. Includes clear, phosphor-coated and self-ballasted
lamps.
Metal Halide Lamp: A high intensity discharge (HID) lamp in
which the major portion of the light is produced by radiation from
mercury. Includes clear, phosphor-coated and self-ballasted lamps.
Nadir: Vertically downward directly below the luminaire or lamp;
designated as 0°.
Outlet Box: See Junction Box.
‘PAR’ Lamps: Parabolic aluminized reflector lamps that offer excel-
lent beam control, come in a variety of beam patterns from very
narrow spot to wide flood, and can be used outdoors unprotected
because they are made of ‘hard’ glass that can withstand adverse
weather.
Parabolic Louvers: A grid of parabolic shaped baffles that redirects
light downward and provides very low luminaire brightness.
Penumbra: The darkest part of a shadow.
Plug-in Wiring: Electrical distribution system which has quick-
connect wiring connectors.
Point Method Lighting Calculation: A lighting design procedure for
predetermining the illuminance at various points in a lighting instal-
lation by use of luminaire photometric data.
Polarization: The process by which the transverse vibrations of light
waves are oriented in a specific plane. Polarization may be obtained
by using either transmitting or reflecting media.
Power Factor: Ratio of: watts/volts ⫻ amperes. Power factor in
lighting is primarily applicable to ballasts. Since volts and watts are
usually fixed, amperes (or current) will go up as power factor goes
down. This necessitates the use of larger wire sizes to carry the
increased amount of current needed with low power factor (LPF)
ballasts. The addition of a capacitor to a LPF ballast converts it to
a HPF ballast.
Preheat Fluorescent Lamp: A fluorescent lamp designed for opera-
tion in a circuit requiring a manual or automatic starting switch to
preheat the electrodes in order to start the arc.
‘R’ Lamps: Reflectorized lamps available in spot (clear face) and
flood (frosted face).
Rapid Start Fluorescent Lamp: A fluorescent lamp designed for

operation with a ballast that provides a low-voltage winding for
preheating the electrodes and initiating the arc without a starting
switch or the application of high voltage.
Raw Footcandles: See Footcandles.
Reflectance: Sometimes called reflectance factor. The ratio of
reflected light to incident light (light falling on a surface).
Reflectance is generally expressed in percent.
Reflected Glare: Glare resulting from specular reflections of high
luminances in polished or glossy surfaces in the field of view. It
usually is associated with reflections from within a visual task or
areas in close proximity to the region being viewed.
Reflection: Light striking a surface is either absorbed, transmitted,
or reflected. Reflected light is that which bounces off the surface,
and it can be classified as specular or diffuse reflection. Specular
reflection is characterized by light rays that strike and leave a surface
at equal angles. Diffuse reflection leaves a surface in all directions.
Refraction: The process by which the direction of a ray of light
changes as it passes obliquely from one medium to another in which
its speed is different.
Romex: A 60°C cable comprised of an outer flexible plastic sheath-
ing that contains two or more insulated wires, designated as type
‘NM’. Romex is normally restricted to residential use.
Room Cavity Ratio (RCR): A numerical relationship of the verti-
cal distance between work plane height and luminaire mounting
height to room width and length. It is used with the zonal cavity
method of calculating average illumination levels.
Rough Service Lamps: Incandescent lamps designed with extra
filament supports to withstand bumps, shocks and vibrations with
some loss in lumen output.
Service Entrance: Point at which power utility wires enter a building.
Shielding: An arrangement of light-controlling material to prevent
direct view of the light source.
Shielding Angle (of a luminaire): The angle from the horizontal at
which a light source first becomes visible. It is the complementary
angle of the cut-off angle. In the case of a luminaire shielded by a
reflector or parabolic cell louver, it is important to ascertain also
the shielding angle to the reflected image of the light source, as this
is often almost as bright as the source itself.
Glossary 141

Silvered Bowl Lamps: Incandescent ‘A’ lamps with a silver finish
inside the bowl portion of the bulb. Used for indirect lighting.
Spacing Ratio (SR): The ratio of the distance between luminaire
centers to the height above the work plane. The maximum spacing
ratio for a particular luminaire is determined from the candlepower
distribution curve for that luminaire and, when multiplied by the
mounting height above the work plane, gives the maximum spacing
of luminaires at which even illumination will be provided.
Spectral Energy Distribution (SED) Curves: A plot of the level of
energy at each wavelength of a light source.
Sphere Illumination: The illumination on a task from a source
providing equal luminance in all directions about that task, such as
an illuminated sphere with the task located at the center.
Task: That which is to be seen. The visual function to be performed.
Task Lighting: Lighting directed to a specific surface or area that
provides illumination for visual tasks.
Three-way Lamps: Incandescent lamps that have two separately
switched filaments permitting a choice of three levels of light.
Transformer: An AC device to raise or lower electric voltage.
Transmission: The passage of light through a material.
Tungsten Halogen Lamp: A gas-filled tungsten incandescent lamp
containing a certain proportion of halogens.
Veiling Reflections: The reflections of light sources in the task that
reduce the contrast between detail and background (e.g. between
print and paper) thus imposing a ‘veil’ and decreasing task visibil-
ity.
Vibration Service Lamps: See Rough Service Lamps.
Visual Comfort Probability (VCP): A discomfort glare calculation
that predicts the percent of observers positioned at a specific
location, (usually 4 ft, or 1.2 m, in front of the center of the rear
wall), who would be expected to judge a lighting condition to be
comfortable. VCP rates the luminaire in its environment, taking
into account such factors as illumination level, room dimensions
and reflectances, luminaire type, size and light distribution, number
and location of luminaires, and observer location and location and
line of sight. The higher the VCP, the more comfortable the light-
ing environment. IES has established a value of 70 as the minimum
acceptable VCP.

Visual Edge: The line on an isolux chart which has a value equal
to 10% of the maximum illumination.
Visual Field: The field of view that can be perceived when the head
and eyes are kept fixed.
Volt (V): The unit for measuring electric potential. It defines the
force or pressure of electricity.
Wall Wash Lighting: A smooth even distribution of light over a
wall.
Watt (W): The unit for measuring electric power. It defines the
power or energy consumed by an electrical device. The cost of
operating an electrical device is determined by the watts it consumes
times the hours of use. It is related to volts and amps by the follow-
ing formula: Watts = Volts ⫻ Amps.
Work Plane: The plane at which work is done, and at which illumi-
nation is specified and measured. Unless otherwise indicated, this
is assumed to be a horizontal plane 30 in. (76 cm) above the floor.
Zonal Cavity Method Lighting Calculation: A lighting design proce-
dure used for predetermining the relation between the number and
types of lamps or luminaires, the room characteristics, and the
average illuminance on the work plane. It takes into account both
direct and reflected flux.
Glossary 143

(References to diagrams, tables and
illustrations are in italic)
absorption 2, 5, 7, 133
accent lighting 28, 31, 37, 87–90, 122,
133
aging, effects on the human eye 4
air conditioning 130, 132
ambient lighting 31, 37, 68–82, 133
American National Standards Institute
(ANSI) 34, 118
American Society for Testing and
Materials (ASTM) 118
American Society of Heating,
Refrigeration, and Air conditioning
Engineers (ASHRAE) 59
ANSI (American National Standards
Institute) 34, 118
Architectural Graphic Standards 113
artificial light see lamps
ASHRAE (American Society of Heating,
Refrigeration, and Air conditioning
Engineers) 59
ASTM (American Society for Testing and
Materials) 118
atrium lighting 35
baffles 45, 45, 134
ballast factor (BF) 53
ballast transformers 28
ballasts 133
constant wattage 42, 43
dimming 103, 121, 135
disposal 129
electronic fluorescent 40–1, 103,
120–1
fluorescent 40–1
high intensity discharge (HID) 32,
41–3, 43, 98
high reactance autotransformer 42, 43
hybrid fluorescent 40
magnetic fluorescent 40, 103
reactor 41–2, 43
battery systems 90
‘batwing’ distribution 49, 49, 134
beam spreads 89, 134, 122
blue shift 4
brightness see luminance
brightness ratio 12
budgets, power 59–63
calculations
computerized 55–8
load 98
zonal cavity 50–5, 58, 76–7, 80, 143
candelas 9, 134
candlepower 9, 11, 134
candlepower distribution curves 49, 49,
134
capacitors 40, 134
casino lighting 62
chemical light 19
church lighting 103
CIE (Commission Internationale de
l’Eclairage) 23
circuit breakers 95–6, 98, 134
classifications, luminaire 46–8, 47
classroom lighting 106
coefficient of utilization (CU) 50, 52,
135
color
perception 2, 3, 3–4
rendition 12, 23–4, 34
temperature 22–3, 83, 135
Index

color rendering index (CRI) 24, 68, 83,
135
commercial lighting 28
Commission Internationale de l’Eclairage
(CIE) 23
compact fluorescent lamps 30, 73, 81,
86, 87, 122
computerized calculations 55–8
computers, use of 103, 107, 113, 132
see also Internet
condensers see capacitors
conduits 100, 101
conference room lighting 83–90, 106,
107–8
constant wattage ballasts 42, 43
Construction Specifications Institute (CSI)
116
consumption of energy see energy
consumption
contactors 103–4
continuous spectrum 20
contract documents 111–25
contractors, electrical 111, 115
contrast 12, 8, 135
controls 58, 62–3, 100–6
correlated color temperature 22, 24,
28–9, 34, 35
corridor lighting see hallway lighting
cosine law of incidence 10, 50, 55
cove lighting 48, 48
CRI (color rendering index) 24, 68, 83,
135
CSI (Construction Specifications Institute)
116
diffusers 45–6, 127, 129
diffusion 12
dimming 58, 102–3, 121, 122–3
accent lights 90
computerized systems 108
incandescent lamps 25, 28
fluorescent lamps 31
for task lighting 83, 85, 87
dimming ballasts 103, 121, 135
direct illumination 46–8, 47
disability glare 11
discomfort glare 11, 136
display lighting 60
downlights 31, 37, 44, 85–7, 86, 88,
89–90
electromagnetic interference (EMI) 41
electromagnetic spectrum 2, 2
electronic fluorescent ballasts 40–1, 103,
120–1
elliptical reflectors 44, 45, 136
emergency lighting 59, 90, 92, 108, 123,
124
energy consumption 59–63, 60, 61, 75,
130, 132
Energy Policy Act 1992 (EPACT 92) 63,
127
ENLIGHTEN (computer program) 131,
132
environmental pollutants see pollutants
Environmental Protection Agency (EPA)
129
EPACT 92 (Energy Policy Act 1992) 63,
127
equivalent sphere illumination (ESI) 13,
136
exit signs 92, 123, 124
eye, human 1–4, 3
filament lamps see incandescent lamps
fixtures, lighting see luminaires
flicker 41, 76
floodlighting 39, 136
fluorescent ballasts 40–1
fluorescent lamps 22–3, 23, 28–31, 29,
121–2, 136
fluorescent luminaires 51
flux 9, 136
footcandles 9, 63, 137
generators, emergency 90
glare 11–12, 68, 71, 83, 89, 137
glitter 15–16, 16
gymnasium lighting 32
hallway lighting 82, 105, 108
hangers 124
high intensity discharge (HID) ballasts
32, 41–3, 43, 98
high intensity discharge (HID) lamps
32–9, 33, 34, 39, 137
high output (HO) fluorescent lamps 28,
30, 137
high pressure sodium lamps 33, 34,
37–9, 39, 138
high reactance autotransformer ballasts
42, 43
housings, luminaire 46
hybrid fluorescent ballasts 40
146 Index

hybrid sodium vapor lamps 37–8
IES Lighting Handbook 63–5, 64
Illuminating Engineering Society (IES)
46, 56, 59, 118
incandescence 20, 20
incandescent lamps 22, 24–8, 25, 26,
122, 138
indirect illumination 47, 48
industrial lighting 37
infrared 2, 27, 105
installation 124–5
instant start fluorescent lamps 28, 29,
40, 138
insulation 87, 98
interference, electromagnetic 41
Internet ix-x, 55, 70–1, 72, 74, 75
see also computers, use of
inverse square law 8, 9–10, 9, 138
Joule heating 20, 138
lamp lumen depreciation (LLD) 53, 75,
138
lamps 138
fluorescent 22–3, 23, 28–31, 29,
121–2, 136
high intensity discharge (HID) 32–9,
33, 34, 39, 137
high output (HO) fluorescent 28, 30,
137
high pressure sodium 33, 34, 37–9,
39, 138
hybrid sodium vapor 37–8
incandescent 22, 24–8, 25, 26, 122,
138
infrared reflecting 27
instant start fluorescent 28, 29, 40, 138
low pressure sodium 34, 39, 39, 139
mercury vapor 21, 22, 33, 34, 34–5,
39
metal halide 33, 34, 35–7, 140
pulse start 35–6, 39
quartz 37
rapid start fluorescent 28, 29, 29, 40,
141
retrofitting 129–30
three-way 102, 102, 142
tungsten halogen 26–7, 142
lenses 6, 139
life safety 90, 92
Life Safety Code 59, 90
light as ‘building material’ 1
light loss factor (LLF) 74, 78, 127, 138
light mechanics 4–7
light-sensitive controls 105
Lithonia Lighting Co. ix, 55, 71
loading docks, lighting for 39
loads, lighting 95, 96, 98, 108–9, 109
low pressure sodium lamps 34, 39, 39,
139
LUMEN MICRO (computer program) 55
lumens 9, 139
luminaire dirt depreciation (LDD) 53,
77, 139
luminaires 43–9, 139
selection 68–80, 83–93, 91, 92
luminance 8, 9, 10, 134, 139
see also glare
magnetic fluorescent ballasts 40, 103
mechanical light 19–20
mercury 28, 31
mercury vapor lamps 21, 22, 33, 34,
34–5, 39
metal halide lamps 33, 34, 35–7, 140
modification of light 4–5, 5
mood creation 28, 68
National Electric Code (NEC) 59
National Fire Protection Association
(NFPA) 59, 118
occupancy sensors 58, 105–6, 107,
123–4, 125
office lighting 47–8, 68–80, 106, 107,
130, 131–2
old age, effects on the human eye 4
outdoor building lighting 37
panelboards 95–7, 96, 97, 107
parabolic diffusers 71, 72, 83, 84
parabolic reflectors 44, 44, 45, 47
parking lots, lighting for 39
PCBs (polychlorinated biphenyls) 129
Philips 75
photocells 58, 104
photoluminescence 21–2, 21, 28, 32
photometrics 56, 57, 72, 74, 74, 77–80
planes of brightness 14, 14
plans 113–16, 112, 114, 117
pollutants 131, 132
see also PCBs (polychlorinated
biphenyls)
Index 147

prisms 6
psychology of lighting 13–16, 130
pulse start lamps 35–6, 39
Purkinje effect 4
quality of light 11–13
quantity of light 9–11
quartz 27
quartz lamps 37
raceways see conduits; wiring
railroad yards, lighting for 39
rapid start fluorescent lamps 28, 29, 29,
40, 141
reactor ballasts 41–2, 43
reflection 2, 5, 6–7, 7, 141
reflectors 26, 26, 43–4, 44, 45, 127,
128–9
refraction 6, 6, 141
relative visual performance (RVP) 13
representatives, manufacturers’ 70–1
restroom lighting 106
retail facilities, lighting for 28, 37, 62
retrofitting 63, 128–32, 130, 131
rheostats 25, 103
room cavity ratio (RCR) 52, 141
safety 59, 90, 92
SED (spectral energy distribution) curves
20, 20, 21, 21, 23
seismic requirements 124
semi-direct illumination 47, 48
semi-indirect illumination 47, 48
shadows 14–15, 15
shielding 44–5, 141
sight, human 1–4
solenoids 103
specifications 116–25
spectral energy distribution (SED) curves
20, 20, 21, 21, 23
spectrum, continuous 20
spectrum, electromagnetic 2, 2
sports facilities, lighting for 37
see also gymnasium lighting
Standard 90.1 59–63
street lighting 38, 39
submittals, contractor’s 119–20
substitutions 115
switches 58, 100–2, 102, 107, 108
see also contactors
symbols, drawing 113, 113
task lighting 47, 83–7, 142
THD (total harmonic distortion) 41,
119, 121
theater lighting 30, 62, 103
three-way lamps 102, 102, 142
timers 58, 104–5
total harmonic distortion (THD) 41,
119, 121
track lights 87
transformers, ballast 28
transmission 5, 5, 142
tungsten halogen lamps 26–7, 142
ultraviolet 2, 21, 28, 34, 35, 37
Underwriters Laboratories Inc. (UL) 118
VCP (visual comfort probability) 13, 142
veiling reflections 11, 142
very high output (VHO) fluorescent lamps
28, 30
visibility 8
vision, human 1–4
VISUAL (computer program) 55, 56
VISUAL BASIC (computer program) 55,
56, 57, 72, 78, 78, 79, 82, 85
visual comfort probability 13, 142
VISUAL PRO (computer program) 56,
80
visually impaired people, lighting for 62
voltages 94
wallwashing 89, 89, 122, 143
warehouse lighting 32, 37, 39, 62, 105
wiring 95, 98–9, 99, 101, 113–15, 114
work planes 68, 143
zonal cavity calculations 50–5, 58, 76–7,
80, 143
148 Index

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