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Illumination Fundamentals - Lighting Research Center

Illumination FundamentalsThe LRC wishes to thank Optical Research Associates for funding this booklet topromote basic understanding of the science of light and and Figures 2-3 and 2-5 are from Physics for Scientists and Engineers, copyright (c) 1990 byRaymond A. Serway, reproduced by permission of Harcourt, portion of this publication or the information contained herein may be duplicated orexcerpted in any way in other publications, databases, or any other medium without expresswritten permission of the publisher. Making copies of all or part of this publication for anypurpose other than for undistributed personal use is a violation of United States copyright laws.

4 Illumination Fundamentals Contents 1. Light and Electromagnetic Radiation ... The Illuminating Engineering Society of North America (IESNA) defines light as

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Transcription of Illumination Fundamentals - Lighting Research Center

1 Illumination FundamentalsThe LRC wishes to thank Optical Research Associates for funding this booklet topromote basic understanding of the science of light and and Figures 2-3 and 2-5 are from Physics for Scientists and Engineers, copyright (c) 1990 byRaymond A. Serway, reproduced by permission of Harcourt, portion of this publication or the information contained herein may be duplicated orexcerpted in any way in other publications, databases, or any other medium without expresswritten permission of the publisher. Making copies of all or part of this publication for anypurpose other than for undistributed personal use is a violation of United States copyright laws.

2 2000 Rensselaer Polytechnic Institute. All rights Coordinator: John Van DerlofskeAuthor: Alma E. F. TaylorGraphics: Julie Bailey and James GrossLayout: Susan J. SechristCover Design: James GrossTechnical Reviewers: Dr. Mark Rea and Dr. John Van Derlofske of the LightingResearch Center ; Dr. William Cassarly and Stuart David of Optical ResearchAssociates. Illumination Fundamentals 34 Illumination and Electromagnetic What is Light?.. The Visible Ultraviolet Infrared Concepts in Refraction (Snell s law).. 10 Reflection and the Index of 12 Total Internal Reflection (TIR).. (Scattering).

3 Radiometric and Photometric Radiometric and Photometric and Luminous Energy and Energy and Luminous 19 Spectral Luminous Radiant Exitance, Irradiance (Radiant Incidence), and and Luminous Radiometric and Photometric Inverse Square s Cosine Emission and 25 Halogen 27 HID 27 High Pressure Mercury Vapor 28 Metal Halide 29 High Pressure Sodium 30 Xenon 31 Fluorescent 31 Illumination Fundamentals 5 Linear Fluorescent 32 Compact Fluorescent Lamps (CFLs).. (Light-Emitting Diodes).. Lamp Lamp and Ray 37 Sequential Ray 38 Nonsequential Ray Modeling Design & 4310.

4 446 Illumination FundamentalsFigures & TablesFigure The electromagnetic 7 Figure Specular, spread, and diffuse reflectionsfrom a 9 Figure Law of 9 Figure Refraction and Snell s 10 Table Indices of 11 Figure Refraction 12 Figure Total internal 13 Figure Transmitted light 14 Figure Lambert s law of 14 Figure The Beer-Lambert 15 Figure Diffuse transmission and reflectance.. 16 Table Radiometric and photometric quantitiesand 17 Figure Spectral Luminous efficiency functionsV( ) and V ( ).. 18 Figure A 1-steradian solid angle removed froma 19 Figure For a solid angle that measures1 steradian, A = r2.

5 19 Figure 21 Figure Luminous intensity.. 22 Figure Inverse square 23 Figure Lambert s cosine 23 Figure Lambertian 24 Figure Construction of an incandescent 25 Figure Common shapes of incandescent 26 Figure Effect of voltage on lamp life, light output,power, and 26 Figure Construction of a mercury vapor 28 Figure Construction of a metal-halide lamp.. 29 Figure Construction of a high-pressure sodium 30 Figure Typical xenon lamp .. 31 Figure Construction of a linear fluorescent 32 Figure Examples of compact fluorescent 33 Figure Typical LED 33 Table Luminances of common light sources.

6 34 Table Efficacies of common light 35 Figure SPDs of three light 36 Figure Sequential imaging optical 38 Figure Nonsequential Illumination 39 Illumination Fundamentals 71. Light and is Light?To the optical engineer, light is simply a very small part of the electromagneticspectrum, sandwiched between ultraviolet and infrared radiation. The visible portionof the electromagnetic spectrum extends from about 380 to about 780 nanometers(nm), as shown in Figure What distinguishes this part of the electromagneticspectrum from the rest is that radiation in this region is absorbed by the photorecep-tors of the human visual system and thereby initiates the process of Illuminating engineering Society of North America (IESNA) defines light as radiant energy that is capable of exciting the retina and producing a visual sensation.

7 Light, therefore, cannot be separately described in terms of radiant energy or of visualsensation but is a combination of the two. ! " # $$ #% " &$ ' ( ) # # * # + # * $ , -% .. / 0 0 / 1 " Figure The electromagnetic from the IESNA Lighting Handbook - 9th Illumination Visible SpectrumWe generally associate five basic colors with the visible portion of the electromagneticspectrum, as indicated in Figure These colors are not distinct bands, but ratherblend together. See Section 6, Spectrum and Color, for more Ultraviolet RadiationUltraviolet (UV) radiation, sometimes incorrectly referred as UV light, has shorterwavelengths than visible radiation (light), as shown in Figure The CommissionInternationale de l Eclairage (CIE) divides UV radiation into three segments: UV-A(400-315 nm), UV-B (315-280 nm), and UV-C (280-100 nm).

8 The UV-A segment, themost common type of UV radiation, overlaps slightly with the shortest wavelengths inthe visible portion of the spectrum. UV-B is effectively the most destructive UVradiation from the sun, because it penetrates the atmosphere and can injure biologicaltissues. UV-C radiation from the sun would cause even more injury, but it is absorbedby air, so it almost never reaches the Earth s Infrared RadiationInfrared (IR) radiation has slightly longer wavelengths than visible light. The CIE alsodivides the IR region of the electromagnetic spectrum into three segments: IR-A(780 1400 nm), IR-B (1400 3000 nm) and IR-C (3000 106 nm).

9 2. Basic Concepts in OpticsWhen light encounters a surface, it can be either reflected away from the surface orrefracted through the surface to the material beneath. Once in the material, the lightcan be transmitted, absorbed, or diffused (or some combination) by the material. Eachof these properties is discussed in this section. Note that these properties usuallyapply to both light and other forms of electromagnetic radiation. However, to simplifythis discussion, it will be limited to ReflectionThere are three general types of reflection: specular, spread, and diffuse, as shown inFigure A specular reflection, such as what you see in a mirror or a polishedsurface, occurs when light is reflected away from the surface at the same angle as theincoming light s angle.

10 A spread reflection occurs when an uneven surface reflectslight at more than one angle, but the reflected angles are all more or less the same asthe incident angle. A diffuse reflection, sometimes called Lambertian scattering ordiffusion, occurs when a rough or matte surface reflects the light at many differentangles. For more information about spread and diffuse reflection, see Section , Diffusion (Scattering). Illumination Fundamentals 9 2 3 $ " 4 5 $ 62 % $ $ " 4 5 2 $ " 4 ""$ Figure Specular, spread, and diffuse reflections from a reflections demonstrate the law of reflection, which states that the anglebetween the incident ray and a line that is normal (perpendicular) to the surface isequal to the angle between the reflected ray and the normal.


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