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Abstract
This front matter contains an introduction, table of contents, and glossary of symbols.

Introduction to the Series

Welcome to the SPIE Field Guides—a series of publications written directly for the practicing engineer or scientist. Many textbooks and professional reference books cover optical principles and techniques in depth. The aim of the SPIE Field Guides is to distill this information, providing readers with a handy desk or briefcase reference that provides basic, essential information about optical principles, techniques, or phenomena, including definitions and descriptions, key equations, illustrations, application examples, design considerations, and additional resources. A significant effort will be made to provide a consistent notation and style between volumes in the series.

Each SPIE Field Guide addresses a major field of optical science and technology. The concept of these Field Guides is a format-intensive presentation based on figures and equations supplemented by concise explanations. In most cases, this modular approach places a single topic on a page, and provides full coverage of that topic on that page. Highlights, insights, and rules of thumb are displayed in sidebars to the main text. The appendices at the end of each Field Guide provide additional information such as related material outside the main scope of the volume, key mathematical relationships, and alternative methods. While complete in their coverage, the concise presentation may not be appropriate for those new to the field.

The SPIE Field Guides are intended to be living documents. The modular page-based presentation format allows them to be easily updated and expanded. We are interested in your suggestions for new Field Guide topics as well as what material should be added to an individual volume to make these Field Guides more useful to you.

John E. Greivenkamp, Series Editor

College of Optical Sciences

The University of Arizona

The Field Guide Series

Field Guide to Geometrical Optics, John E. Greivenkamp (FG01)

Field Guide to Atmospheric Optics, Larry C. Andrews (FG02)

Field Guide to Adaptive Optics, Robert K. Tyson & Benjamin W. Frazier (FG03)

Field Guide to Visual and Ophthalmic Optics, Jim Schwiegerling (FG04)

Field Guide to Polarization, Edward Collett (FG05)

Field Guide to Optical Lithography, Chris A. Mack (FG06)

Field Guide to Optical Thin Films, Ronald R. Willey (FG07)

Field Guide to Spectroscopy, David W. Ball (FG08)

Field Guide to Infrared Systems, Arnold Daniels (FG09)

Field Guide to Interferometric Optical Testing, Eric P. Goodwin & James C. Wyant (FG10)

Field Guide to Illumination

In writing this Field Guide to Illumination, the first task was to decide what topics to include. Illumination tends to mean different things to different people. Certainly any subject matter under the purview of the CIE, Commission Internationale de l’Eclairage (the International Commission on Illumination) or the Illuminating Engineering Society of North America (IESNA) must be considered. Some particular areas pertaining to imaging systems and nonimaging optics are potentially overlooked. Thus, we chose to address a number of topics that fall under the following three categories: imaging system illumination, nonimaging optics for illumination, and architectural illumination, which all call upon principles of radiometry and photometry. Although this is not a guide to radiometry, enough information on the subject is included to make this manual a self-contained document. Additionally, those optical properties of materials that are pertinent to illumination, such as surface color, scattering, and retroreflection are described.

The content in this Field Guide starts with traditional illumination in imaging systems, followed by the recent advances in computer-aided design of high efficiency nonimaging illumination optics, along with the modern source models that support these techniques. Sections on the illumination of visual displays are included.

There was not enough room for a complete treatment of architectural illumination, but some important topics are included at the end of this Field Guide such as indoor and outdoor architectural illumination.

The notation and terminology are consistent throughout this Guide, but we do not lose sight of the fact that they may not be consistent in the field. Examples of alternate notation and terminology are presented.

Angelo ArecchiTahar MessadiR. John Koshel
Hebron, NHFayetteville, ARTucson, AZ

Table of Contents

Glossary ix

Basic Quantities in Illumination 1

Flux and Irradiance 1

Solid Angle 2

Intensity, Radiance, Projected Solid Angle 3

Solid Angle and Projected Solid Angle 4

Spectroradiometric and Radiometric Quantities 5

Photometric Quantities 6

Matrix of Basic Quantities 7

Photopic and Scotopic Vision 8

Luminous Efficacy 9

Typical Values of Illumination Quantities 10

Averaged LED Intensity 11

Color 12

Light Source Color 12

Chromaticity Diagram 13

Color Temperature and CCT 14

Dominant Wavelength and Purity 15

Surface Color 16

Color of Fluorescent Surfaces 17

Color Rendering and CRI 18

Calculating CRI and Problems with CRI 19

Sources for Illumination 20

Typical Source Parameters 20

Tungsten Lamps 21

Tungsten and Sunlight 22

Fluorescent Lamps 23

H.P. Sodium and Metal Halide 24

Xenon and White LED 25

Light Emitting Diodes (LEDs) 26

Illumination Properties of Materials 27

Transmittance, Reflectance, and Absorptance 27

Reflectance Factor and BRDF 28

Harvey / ABg Scatter Model 29

Directional Properties of Materials 30

Retroreflectors—Geometry 31

Retroreflectors—Radiometry 32

Illumination Transfer 33

Lambertian and Isotropic Models 33

Known Intensity 34

Known Flux and Known Radiance 35

Form Factor and Average Projected Solid Angle 36

Configuration Factor 37

Useful Configuration Factor 38

Useful Form Factor 39

Irradiance from a Uniform Lambertian Disk 40

Cosine Fourth and Increase Factor 41

Known Irradiance 42

ω, Ω, NA, and f/# for a Circular Cone 43

Invariance of Radiance 44

Illumination in Imaging Systems 45

Image Radiance 45

Limitations on Equivalent Radiance 46

Image Irradiance 47

f/#, Working f/#, T/# NA, Ω 48

Flux and Étendue 49

Illumination in Nonimaging Systems 50 50

Generalized Étendue 50

Concentration 51

Skew Invariant 52

Fibers, Lightpipes, and Lightguides 53

Fibers-Basic Description 53

Numerical Aperture and Étendue 54

Fiber Bundles 55

Tapered Fibers and Bundles 56

Classical Illumination Designs 57

Spherical Reflector 57

Abbe Illumination 58

Köhler Illumination 59

Ellipsoidal and Paraboloidal Mirrors 60

Spectral Control and Heat Management 61

Illumination in Visual Afocal Systems 62

Uniform Illumination 63

Searchlight 63

Source at a Distance 64

Mixing Rod 65

Bent Lightpipes 66

Integrating Sphere 67

Lenslet Arrays 68

Small Reflectors, Lenslet Arrays, and Facets 69

Source Models 70

Source Modeling Overview 70

Source Modeling Methods 71

LED Modeling 72

Incandescent Lamp Modeling 73

Arc and Fluorescent Lamp Modeling 74

Nonimaging Compound Concentrators 75

Nonimaging Compound Concentrators 75

Concentrators as Luminaires 76

Compound Parabolic Concentrators 77

Compound Elliptical and Hyperbolic Concentrators 78

Tailored-Edge-Ray Design 79

Faceted Reflector Design 80

Advanced Nonimaging Optic Design 81

Displays 82

Displays—Overview 82

Backlit Display Components 83

Backlit Display: Source and Injector 84

Backlit Display: Lightguides, Features, Reflectors 85

Backlit Display: Polarizers, LC, and BEF 86

Projection Displays 87

Characterizing Illumination Systems 88

Mapping Flat-Fielding Sources 88

Goniophotometers 89

Types A, B, C Goniometer Coordinate Systems 90

“Snapshot” Goniophotometers 91

Software Modeling 92

Software Modeling Discussion 92

Architectural Illumination 93

Role of Light in Architecture 93

Light and Visual Performance 94

Eye Adaptation and Visual Fields 94

Apparent Brightness 95

Lighting Design 96

Lighting Design—Layering of Light 96

Luminaire for Open-Plan Office 97

Photometric Report and VCP 97

Spacing Criteria and Coefficient of Utilization 98

Daylight Compensation 99

Daylight Factor 99

Daylight Strategies 100

Exterior Lighting 101

Nighttime Visibility Criteria 101

Recommended Illuminance for Façades 102

Façade Floodlighting for Uniform Illumination 103

Illumination of Outdoor Areas 104

Special Considerations for Outdoor Fixtures 105

Parking 106

Outdoor Luminaire-Transverse Light Distribution 106

Outdoor Luminaire-Lateral Light Distribution 107

Roadway Lighting 108

Criteria for Roadway Lighting 108

Small Target Visibility 109

Recommended Roadway Luminaires 110

Recommended Lamps for Roadway Luminaires 111

Appendix 112

Equation Summary 112

CIE Illuminants A and D65 119

x¯, y¯, z¯, V(λ), and V′(λ) 122

Archaic and Arcane Units of Illumination 125

Bibliography 127

Glossary

α

Absorptance

α

Observation angle (in retroreflection)

ai

Input area to a compound concentrator

ao

Output area of a compound concentrator

A

Absorbance

Ai

Illuminated area

Ar

Radiating area

ax

Area of plane x

aΩ

Throughput, étendue

C

Concentration ratio

CCT

Correlated color temperature

CIE

International Commission on Illumination

CRI

Color rendering index

di

Diameter of input aperture to a CPC

do

Diameter of output aperture of a CPC

ds

Diameter of small aperture of a CPC

D(μ, λ)

Donaldson matrix

E

Irradiance

E

Illuminance normal to the illumination

E0

Axial irradiance

Ee

Edge irradiance

Ei

Image irradiance

Ei0

Axial image irradiance

Eλ

Spectral irradiance

f/#

F-number

f/#w

Working F-number

F′

Increase factor

Fa to b

Form factor from a to b

fskew

Skew invariant

I

Intensity

ILED A

Averaged LED intensity, CIE condition A

ILED B

Averaged LED intensity, CIE condition B

Iλ

Spectral intensity

L

Radiance

L*, a*, b*

CIE 1976 (L* a* b*) color space; CIELAB

L*, u*, v*

CIE 1976 (L* u* v*) color space; CIELUV

Li

Image radiance

L0

Object radiance

Lλ

Spectral radiance

M

Integrating sphere multiplier

m

Lateral image magnification

n

Index of refraction

NA

Numerical aperture

OD

Optical density

pe

Purity

pf

Packing fraction

psa

Projected solid angle

R

Reflectance factor

RA

Coefficient of retroreflection

Ra

General color rendering index

RI

Coefficient of retroreflected luminous intensity

RL

Coefficient of retroreflected luminance

Sλ(λ)

Spectral density of a light source

T

Transmittance factor

T/#

T-number

u, v

CIE 1960 UCS chromaticity coordinates

u′, v′

CIE 1976 UCS chromaticity coordinates

V(λ)

Photopic luminous efficiency

V′(λ)

Scotopic luminous efficiency

W*U*V*

CIE 1964 uniform space coordinates

x, y

CIE 1931 chromaticity coordinates

X, Y, Z

CIE tristimulus values

x¯, y¯, z¯

CIE color matching functions

β

Entrance angle (in retroreflection)

ξ

Generalized étendue

λ

Wavelength, emission wavelength

λ0.5m

Center wavelength (for LED)

λc

Centroid wavelength (for LED)

λd

Dominant wavelength

λp

Peak wavelength (for LED)

μ

Excitation wavelength

ρ

Reflectance

ρ¯

Average reflectance

τ

Transmittance

U

Viewing angle (in retroreflection)

Φ

Flux

Φλ

Spectral flux

Ω

Projected solid angle (psa)

ω

Solid angle

Ω¯ a to b

Average projected solid angle from a to b

Ωi

Input psa to a compound concentrator

Ωo

Output psa from a compound concentrator

Ωx

Projected solid angle viewed from plane x

θi

Input half-angle of compound concentrator

θo

Output half-angle from compound concentrator

θmax

Maximum output half-angle from CPC

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