GE Light & Color Brochure 1978

7/30/2019 GE Light & Color Brochure 1978

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TP-1 19LIGHTING BUSINESS GROUP

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THE NATURE OF LIGHT"Light" is a special,magnetic energy." It isalone can stimulate the

narrow range of electro-a special range because ittwo types of receptors with-

TIGHT AND ENERGYElectromagnetic energy is only one form of energyknown today. Other forms are thermal, chemical,kinetic, atomic, electrical, etc. Electromagnetic en-ergy is also referred to as radiant energy because itexists only in the form of repeating wave patternstraveling in straight paths, as rays, in all directionsfrom its source. So light, being a special form ofradiant energy, also is called "visible radiantenergy. "

Considering that energy cannot be destroyed -only changed from one form to another, and con-sidering the physiological composition and functionsol the eye, we can now understand that Iight istransformed from electricai energy to radiant elec-tromagnetic energy within a light source, travels ina high-speed, high-frequency wave form, and be-comes useful to man when a sufficient amount ofit is transformed into chemical energy within thereceptors of the eye.There is a very broad spectrum of radiant,electromagnetic energy, of which light is but onenarrow band. All radiant energy travels at the speedof 3x108 meters per second (186,000 miles per sec-ond) in air or in a vacuum. At one end of thespectrum are cosmic rays, and at the opposite endare electrical power waves. The individual types ofradiant energy are identified by their particularranges of frequencies, or number of wave cycles persecond. The average wavelength of the shortest

* Both the Electromagnetrc Wave Theory and the Quantum Theory have been pos-tulated as possible explanati0ns f0r the phen0menon of radiant energy. While sciencehas proven neither, t0 date, lhe Electromagnetic Wave The0ry provides the m0stdirect explanation 0f radiant energy characteristics,

in the eye which permit vision. Therefore, we callIight "visible energy," even though we cannot seethe energy itself.

cycles of radiant energy known (cosmic rays) is0.00001 nanometers. (One inch contains about25.4 million nanometers. A nanometer is onethousand-millionth of a meter.) At the other endof the known spectrum of eiectromagnetic radiationare electric power waves-

with an average wave-Iength of almost 5 million meters (3100 miles).The spectrum of radiant energ'y waves we calllight is very narrow, ranging from approximately380 nanometers to 760 nanometers** (or from 15to 30 millionths of an inch). Wavelengths shorteror longer than these do not stimulate the receptorsin the eye. Beyond this range is darkness, for, whilethe eye may be exposed to many other wavelengthsof radiant energy, they are not capable of initiatingresponses in the eye.LIGHT sOIJRCEsThe sun - and electric lamps, are considered lightsources because they transform energy from anotherform into the radiant energy wavelengths which wecall light. But these light sources also emit usefulenergy at wavelengths both shorter and longer thanlight waves. Ultraviolet energy - valuable for itsgerm-killing, suntanning, and photochemical prop-erties, has wavelengtlx shorter than light waves;and infrared energy waves (often referred to asheat rays) are longer than light waves. All radiantenergy, when absorbed, can be transformed intoheat.+* S0me authorities extend the visibie t0 780 nanometers. The effect on seeing 0fthese longer wavelengths is very close to zero.


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THE COLOR SPECTRUMA light source emitting radiant energy relativelybalanced in all visible wavelengths will appearwhite to the eye. However, passing a narrow beamof white light through a prism of transparent mate-rial will spread and separate the individual wave-lengths of visible energy so that the eye can dis-tinguish between them - the resulting visual phe-nomenon is called a color spectrum. The normaleye will see three wide bands of blended color -violet, green, and red, with several narrower bands(blue, yellow, and orange) blended between thewider bands. The "color blind" eye will see onlyRepresentation of a prism bendingrays of white light. The effect ofthe prism is to bendshorterwave-lengths more than longer wave-lengths - separating them intodistinctly identifiable bands ofcolor. The colors can be recom-bined into a beam of white lightby accurately orienting a properlydesigned second prism to inter-cept the dispersed color lightrays. Note that the prism also isuseful for separating infrared andultraviolet rays as well as visiblerays.

VISIBLE SPECTRUM

graduations of gray, or perhaps some of the colorsand some gray - depending upon the extent ofphysiological impairment of the eye.A lamp designer is more concerned with the causeof these wavelengths than he is with the names wehave given them. However, it is vitally importantthat he know that wavelengths longer than 610nanometers produce that effect we call "red" - andthose between 440 and 500 nanometers are called"blue," and so on, in order to control both theappearance of light sources themselves and theeffects light sources have on the appearance ofcolors in objects around us.

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We call radishes "red," Iemo4s "yellow," andpine trees "green" - in lact we have assigncd colornames to almost everything we come in contactwith in our daily lives. That these objects appear tobe the same colors under all lighting conditions iscalled "color constancy" - which simply meansthat those objects consistently reflect or transmitiight waves only in a particular, narrow color rangcwhile absorbing all others. Water has no colorconstancy because it will reflect and transmit a//light waves, hencc, it appears to be whatevcr coloris dominant in its surroundings.The two fundamental ways in which objects andmediums modify the colors of light have alreadybeen mentioned-transmission and reflection, bulobjects and mediums usually are selectiue in howmuch energy, and at which wavelengths they willtransmit or reflect light. The Selective SpectralTransmission diagram (p. 6) shows how a greenglass filter will selectively absorb all wavelengthsexcept green from a Iight beam passing through it,so that both the chromaticity and luminance of thetransmitted beam are affected.

Just how much the color and intensity of thetransmitted light is modified depends on the molec-ular composition of the materials through whichthe light passes. For example, in some coloredlamps, coatings of colored pigments and dyes areused to selectively absorb unwanted wavelengthsor colors and transmit the desired wavelengths. Inother cases, the glass or medium itself is colored toachieve the same effect.When light is evenly played on a dilfuse (un-polished) surface, the effect is that light waves arercflected in all directions, but only after they have

been modified by the absorption qualities of thesurface. The result is that the surface therr appearsto have a color all its own . . . different from thecolor of the light source. But that is only becausethe surface has absorbed various amounts of variouswavelengths of spectral energ.y. Sandstone is ahighly diffuse material with relatively even spectralabsorption qualities, hence, it appears tan in colorthroughout (see diagram, p. 6). A coat of paintol Ir object also has an evenly distributed qualityof absorbing, and thus will evenly reflect whatevercolors, or wavelengths of energy, that are not ab-sorbed by the paint.It is important to reiterate that since att \ghtwaves are modified in some way by a// physicalobjects - lhat the color appearance of an object isdetermined by the mlx and energy of light waveswhich remain intact to reach our eyes. Objects havea characteristic color only because of the-way theyselectively reflect or transmit or otherwise modifyvarious wavelengths of light.As shown in the reflectance chart below, butterappears "yellow" because it absorbs blue iight andreflects a high percentage of all other colois. Theresultant combination, or dominant wavelength, isyellow. Similarly, lettuce reflects light with *urr.-lengths primarily in the 500 to 600 nanometer(green) range and absorbs most of the energy atother wavelengths. A tomato, then, is red -onlybecause it reflects radiant energy at 610 to 280nanometers while absorbing most of the energy atother wavelengths.

But just as important to the apparent color ofobjects is the character of light waves being ra-diated onto the objects by the light sourct.

500 600WAVELENGTH (Nanometers)

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COLOR PERCEPTIONThe process and mechanisms by which the brain"perceives" color, or any other concept, is notyet fully defined, but science and technolog'y arebeing continually advanced toward that end. Per-haps someday we will understand how we think -"color" - but for the moment we are concernedwith what is already established knowledge in thefield of light and color.The adjacent illustration demonstrates that themore complete definition of color as a concept isaccurate when we consider that color does notexist independent of normal, color vision. As pre-viously mentioned, the totally color-blind personcannot distinguish between various wauelengtb oflight - he can oniy distinguish between variousamlunts of light. To him there is no "color" -everything is either black or white or shades ofgrays in between. N{ost important is the fact thatthe physical light waves received by both a color-blind person - and by a person with normal colorvision, are not changed by the condittlon of thereceptors in the eyes of either person. Only theconceltt (perception or interpretation) of what is seenby each person is changed. Therefore, red, or anyother color, is exclusively the mental concept result-ing from the brain's interpretation of special visualstimuli.COLOR ASSOCIATIONSNow that we have brought color into the realm ofthe abstract concept, it immediately becomes a partof what we think about everything else - objects,situations, attitudes, moods, environmental condi-tions, etc. Color is unconsciously assimilated intoall our impressions or concepts because our eyes arecorstantly supplying our brain with color infor-mation which is automatically associated with allother information on any given subject or situation.

Perhaps more than any other single element indesign, peopie's reactions to color affect their indi-vidual preferences. But, some color reactions areuniversal. Certain colors, for example, are associ-ated with certain moods. Reds, oranges, and yel-lows, are generally accepted as stimulating whileblue, blue-violet, and violet are considered theIeast exciting.People's reactions to the colors associated withmaterials do not always correspond to their re-actions to the same colors associated with light.As a demonstration, the green in foliage is gen-erally accepted as refreshing, cool, and undisturb-ing, so people have come to think of trees andshrubs as somewhat neutral or quiescent in effect;hence, green background materials in man-madeobjects are psychologically restful. But green in alight source is unnatural; and used alone, tends toproduce a macabre or sinister effect.

Where the "proper" appearance of people isimportant, there is a strong unconscious preferencefor white light sources which are rich in red light;these iamps help impart a healthy, ruddy or tannedimpression of the skin and flatter the complexion.There also are indications that people prefer warmIight in areas where lower ievels of illumination areinvolved, while cool light seems to be more accept-able for higher levels.Where stronger, more saturated colors are in-volved, people generally agree that warm colonappear to advance, while cool colors recede andhelp support a feeling of spaciousness. In a moresubtle sense, changes in the color of light appear toalter the moods of a space - the impressions asso-ciated with warm sunlight and cool shadows; thepinks and purples of a sunset; the similar restfulqualities of the interior of a cathedral where light istinted by stained glass windou's; the gaudy, over-stimulating effects of rapidly moving, colored car-

nival lights. People invariably feel the psychologicalimpact of light and color without ever realizing thatthey do - or even analyzing the reasors for associ-ating colors with moods.

"lt's redl"lt is not - it's bright redi No, it's dark! ."Nope - medium darkl"Color ls A Concept That Does Not Existpendent Of Normal Color Vision. lnde-


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GOLOR VISIONThe diagram below briefly summarizes the ingre-dients in the process of seeing light and color. Aswe have seen in the preceding pages, it is a com-plex process involving physics, psychology. engi-neering, photometry, etc. - and now we come tothe eye itself - physiology.

oYE FUNCTIONSThere are many theories to explain the phenomenonof color vision. 'l'he most easily understood rsYoung's three-component theory which assumesthree kinds of light sensitive elements (cones) - eachreceptive to one of the primary colors of light - anextreme spectrum red, an extreme spectrum violet

GENERATORS -TRANSMITTERS(LTGHT SOURCES)

SUN, DISCHARGE LAMPS,FLUORESCENT LAMPS,INCANDESCENT LAMPS,OPEN FLAMES, ETC.

HOW THE EYE WORKSLight waves enter the eye through thecornea which roughly focuses thepattern of waves on the foveal pitin the retina. The waves are fine-fecused as they pass through the lens.The iris acts as a diaphragm whichexpands or contracts the pupil (open-ing in the iris to the lens), controllingthe amount of light that is permittedto enter the eye.The rods and cones are the ultimatereceivers f or individual parts of theimage. They transform the receivedoptical image pattern from radiantenergy into chemical energy whichenergizes millions of nerve endings.The optical pattern then becomes aseries of electrical impulses travelingwithin a very special group of nerveswhich connect to the optic nerve. Theoptic nerves (from both eyes) combineand transmit the selective impulsesto the brain where they are interpreted.

SEEING LIGHT AND COLOR

MODIFIERS AND RETRANSMITTERS(SECONDARY LIGHT SOURCES)

ATMOSPHERE, AIR, WATER, PLANETS, LENSES,WINDOWS, TREES-ALL NATURAL ORMANUFACTURED OBJECTS WHICH MODIFY

LIGHT WAVES BEFORE THEY REACH THE EYE.

RECEIVERS -ENCODERS( EYES)

CORNEA,IRIS, LENS,

RODS & CONES,OPTIC NERVES

DECODER -INTERPRETER(BRATN)

ANALYSIS,IDENTIFICATIONASSOCIATIONPERCEPTION

VERTICAL CROSS SECTIONOF THE EYE

GANGLIONCELLS SYNAPSES CONES

SYNAPSES RODSL''-2--=-'4_---u------

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RETINA


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and an imaginary green (see adjacent sensitivitychart).The cones in each eye number about sevenmiliion. They are located primarily in the centralportion of the retina called the fovea, and arehighly sensitive to color. People can resolve finedetails with these cones largely because each oneis connected to its own nerve end. Muscles con-trolling the eye always rotate the eyeball until theimage of the object of our interest falls on thefovea. Cone vision is known as photopic or day-time vision.Other light receptors. called rods. are

COLOR DEFICIENCIESThe totally color-blind pcrson cannot distinguishbetween color and quantity because thc concs arceither partially or toially impaired - only thc rodsare functioning. This person's eyes are only serxitiveto luminance, or quantity of light. As a result, lightsources appear as "brighter or dimmer," and ob-jects appear as "lighter or darker."A totally color-blind person has full appreciationof his surroundings - but in values of grays, muchas a person with normal color vision has full appreciation of a color TV program which is viewedon a black and white TV set.

REDRECEPTSR

Re lative spectral res-ponse function of thecone mechanisms aspostulated in Young'stheory. Absolute sen-sitivities of the threereceptor peaks arenot necessarily equal.

The most prominent type of color deficiency isknown as Deuteranomaly - or red-green blindness,wherein the person sees yellows and blues normally,but has trouble differentiating reds and greens. Onlyabout five percent of the male population has thisdeficiency, and only 0.38 percent of the females.An even smaller number of people - 0.003 percentmales and 0.002 percent females, are totally colorblind.

BtUERECEPTOR

also pres-GREEN

RECEPTOR

500 600WAVELENGTH (Na nometers)

ent in the eye - but they are not involved incolor vision. Rods serve to give a general, overallpicture of the field of view, and are receptive onlyto the quantity of light waves entering the eye.Several rods are connected to a single nerve end;thus they cannot resolve fine detail. Rods aresensitive to low levels of illumination and enablethe eye to see at night or under extremely lowIighting conditions. Therefore, objects which appearbrightly colored in daylight when seen by thecolor-sensitive cones appear only as colorless formsby moonlight because only the rods are stimulated.This is known as scotopic or night vision.DAY.NIGHT VISIONAs the adjacent spectral sensitivity curves show, theeye is not equally sensitive to all wavelengths. Indim light particularly, there is a definite shift inthe apparent brightness of different colors. This wasdiscoveredbyJohannes von Purkinje. While walkingin the fields at dawn one day, von Purkinje ob-served that blue flowers appeared brighter than red,while in full daylight the red flowers were brighterthan the blue. This is now called the Purkinjeeffect and is particularly important in photometry -the measurement of light.

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VISUAL ILLUSIONS"Now you see it-now you don't." Thegician's line about sleight-of-hand tricks ismore applicable to tricks our eyes play oncolors - in different arrangements, under

old ma-perhapsus withdifferentIighting, at different distances. To get the strongestvisual reactions, cover all other illustrations on thesepages when studying each illusion.

COLOR RECEPTION DEFICIENCIES. Non-func-tioning cones in the eyes of totally color-blind persons result in rod vision only -whereby everything is perceived in blacks.grays, and whites (right half of illustration)instead of in colors (left half of illustration).The values in the grays of the illustrationmatch the combined chroma and values inthe colors.

CHAMELEON EFFECT. Colors of medium valueand chroma will appear to change in thedirection of lighter, brighter colors - or darker,duller colors surrounding it. The blue bars inthis illustration are all printed with exactlythe same color of ink - but they appearlighter next to yellow. and darker next toblack.

DISAPPEARING SPOTS. Stare at the colorblocks and dancing spots will appear wherethe corners meet. But try to look at one ofthe spots and it fades away. What shape arethe spots? Squares, circles, four-pointedstars? rllIIIIIIIIIII:rrrDAY-NIGHT VlSlON. Under good lighting con-ditions the red flower will appear brighter thanthe blue. lf viewed for five to ten minutes invery dim light though, the red flower will al-most disappear while the blue flower willstand out as a light gray. (Look one or twoinches aside from the blue flower to see itmore clearly since the rods (used for scotopic,or night vision) in the eye are most numerousin the retina just outside the foveal pit.)


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ADDITIVE SPATIAL FUSION. The green dotpattern in the shape of the United States willmerge into a solid gray when viewed from adistance of 6 to 8 feet. At that distance, theeye can no longer distinguish individual colors(yellow and green) and the phenomenon pro-duced is "gtay." This same phenomenon isused in all lithographic printing in this book.

ADVANCING AND RECEDING COLORS. Warmcolors and light grays appear to advancetoward the eye while cool colors and darkgrays appear to recede. since this phenome-non is related to day-night vision, both ovalsin this illustration will appear as mounds whenviewed for 5 to 10 minutes in very dim light.

COMPLEMENTARY AFTERIMAGE. To see redand white fireworks in a blue-violet sky,stare for 30 seconds at the black dot justbelow center - then look at the black dotin the white space below. Prolonged con-centration on any colors will reduce eye sen-sitivity to them, and the reverse, or comple-mentary colors, remaining unaffected, willdominate the afterimage for a brief perioduntil balance is restored.

o


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GOLORIMETRYColorimetry is the science of measuring and system-atically designating colors. It is an important sci-ence, since precise systems of color measu-rementare required to identify, duplicate, and standardizethe thousands of colors in use today - and manyuseful systems have been set up to organue andspecify these colors. But before any of the systemscan be described, it is essential to understand therelationship which exists between the primary colorsof light and the primary colors of pigments.PRIMARY AND SECONDARY COLORSThe primary colors of light (red, green and blue)can be added to produce the secondary colors ofIight - magenta (red plus blue), cyan (green plusblue), and yellow (red plus green). Thus, the colorsof light are called "additive." A secondary color ofIight mixed in the right proportions with its oppo-site primary will produce white light. For example,a mixture of yellow and blue light will result inwhite light. Thus, yellow and blue are complemen-tary colors of light - as are cyan and red, andmagenta and green.

In pigments or colorants, however, a primarycolor is defined as one that subtracts or absorbs aprimary color of light and reflects or transmits theother two. So the primary colors in pigments (some-times called subtractive primaries) are magenta,cyan, and yellow - the secondary colors of light.This subtractive nature of pigments is easilydemonstrated by placing magenta, cyan, and yel-low pigment filters over a source of white light(see adjacent illustration). Each of the pigmentfilters absorbs or subtracts one of the primarycolors from the light. Where two filters overlap, oneof the primaries of light is transmitted. For ex-ample, the yellow filter absorbs blue (transmittingred and green) and the magenta filter absorbsgreen (transmitting red and blue). Together, thefilters transmit only red - having, in effect, sub-tracted the other two primary colors from thewhite light. Where the three pigment filters aresuperimposed at the center, all light is absorbed.Complementary pigment colors are the same asthose in light - yellow and blue, cyan and red,magenta and green.

Color television reception is an example of the"additive" nature of light colors. On the interiorface of the picture tube is applied approximately100,000 triangular dot patterns of electron-sensitivephosphors - each triad consisting of one phosphordot each that will radiate red light, blue light, andgreen light, respectively. In operation, all red-emitting phosphor dots in all triads are stimulatedby electron pulses from an electron gun inside thepicture tube which generates 'ored" pulses corres-ponding to "red" energ'y seen by the TV camera.Blue and green electron guns inside the picturetube stimulate the blue and green triad phosphorsin the same manner.The effect, viewed on the home color TV re-ceiver, is that the three primary colors from thephosphors are "added" together and received bythe color sensitive cones in the eye, and a fullcolor image is perceived. Thirty successive imagechanges per second - in all three colors, completethe.motion illusion in color television.THE COLOR TRIANGLEAlthough black and white pigments are not con-sidered true colors, their addition to colored pig-ments produce tints, shades, and tones. The ad-jacent diagram illustrates the triangular relation-ship involved here - that adding black to a pig-ment color produces a shade, whereas adding whiteproduces a tint. When gray (a mixture of blackand white pigments) is added to a color pigment,a tone is produced.


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FULL

THE COLOR TRIANGLE

OSTWALD SYSTEMThe Ostwald notation for"pale blue" would be 1 5ca. The fifteen denotesthe basic colorvivid blue,the "c" denotes the per-centage of white, and the"a" denotes the percent-age of black.

OSTWALD COLOR SYSTEMSimilar in arrangement to the Color Triangle is theOstwald Color System which arranges lettered colorchips in triangles and describes them in terms ofpurity, whiteness, and blackness (adjacent chartprinted with permission of Container Corporationof America). The purest colors (or hues) contain nowhite or black pigments. The system as originallypublished divided the spectrum of colors into 24basic numbered hues with 28 variations of each inIightness or darkness (tints, shades, and tones).MUNSELL COLOR SYSTEMThe Munsell system of color notation is based on atheoretical solid form - much like an irregularglobe. The vertical axis is graduated into nineshades of gray - with black at the bottom as zero,and white at the top as ten (see adjacent illus-tration, printed with permission of the MunsellColor Company). The colors of the spectrum aredivided into 20 basic hues which are representedas vertical pie sections of the solid with their purestcolors located around the perimeter, or equator.The Munsell system also uses a set of coded,standardized color chips for each color. Variablesin the Munsell system are hue, value, and chroma.

Hue is the classification of a color by which theeye sees it as red, blue, green, yellow, etc. AMunsell hue is designated by a single letter - R forred, G for Green, or pairs of letters, such as YG,for yellow-green.Value (sirnilar to the gray scale in the OstwaldSystem) indicates lightness or darkness of a color ona scale ranging from 0 for black to 10 for white.Thus, a color can be dark or light red, indicating a

position in a light-to-dark scale. (Munsell valueis approximately equal to the square root of thepercent reflectance of the color.)Chroma indicates the purity or saturation of thecolor, or conversely, its freedom from dilution.Chroma is indicated by a number preceded by aslant line, following the value notation.

MUNSELL SYSTEMForm of the Munsellcolor solid showingcolor notation scales forhue, value, and chromaand a sample color huechart. A very greyed(low value) yellow wouldbe identified by the no-tation 5Y 3/2.

BLACK

y------------.QUARTER OF SOLIDREMOVED TO SHOWINTERIOR SELECTION


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ISCC.NBS COLOR SYSTEMThe Inter-Society Color Council - National Bureauof Standards (ISCC-NBS) has standarized 267names for describing the colors of paint. Eachname is matched to a color chip, with the bound-aries of each name fixed with limits defined in theMunsell color notation system.

The following 28 basic hue names are used:ISCC.NBS STANDARD HUE NAMES AND ABBREVIATIONS

Abbre-viqtion Abbre.v ioiio nredreddish orongeorongeoronge yellowyellowgreenish yellowyellow greenyellowish greengreenbluish greengreenish bluebluepurplish blueviolet

purplereddish purplepurplish redpurplish pinkpin kyellowish pinkbrownish pinkbrownish orongereddish brownbrownyellowish brownolive brownoliveolive green

RrOoOY

gYYGyGGbGsBBpB

PrPpRpPkPKvPkbrPkbrOrBrBryBrOlBrololG

Additional adverbs, and adjectives are used incombination with the above hue names to com-pletely identify the 267 basic color chips in thesystem. The additional modifiers are: StrongVividBrilliantDeep PaleThe adjacent chart illustrates the application of theISCC-NBS color designation system as applied tothe Munsell notation for Red ranging from 4Rto 6R.C. I. E. COLOR SYSTEMThe C.I.E. color system was devised and adoptedby the C.I.E. (Commission Internationale del'Eclairage - the International Commission on Il-lumination) in 1931 and has since become an inter-national standard for measuring, designating, andmatching colors.In the C.I.E. system, the relative percentages ofeach of the theoretical primary colors (red, green,blue) of a color to be identified are mathematicallyderived, then plotted on a Chromaticity Diagram asone chromaticity point. From the chromaticitypoint, the dominant wavelength and purity can bedetermined. All possibie colors may be designatedon the Chromaticity Diagram, whether they areemitted, transmitted, or reflected. Thus, the C.I.E.

LightMediumDarkVeryGrayishModerate

RED RANCf


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system may be coordinated with all other colordcsignation systems.To specify the chromaticity of a color by theC.I.E. system, it is first necessary to measure thecolor's spectrophotometric vaiues (reflectance, emit-tance, or transmittance) at each wavelength. Thesevalues then must be weighted by the values of thethree theoreticai primaries (see adjacent chart), andthe resultant computation will represent the amountof the theoretical primaries (red, green, and blue)needed to produce for the standard observer thecolor of the spectrum at that wavelength.The sums of each of these calculated red, greenand blue calculations are called the tristimulus ualuesfor that color. Tristimulus values are denoted bycapital letters, X (for red), Y (for green), and Z (forblue). The Y (green) value also is that color'sluminosity. The tristimulus values are then used tocalculate the color's chromaticity coordinates.A color's chromaticity coordinates represent therelative percentages of each of the primary colorspresent in a given color. Lower aasa letters are used

to designate the coordinate values: x : red, y :green, and z : blue. The fractional values areeasily computed from the tristimulus values, X, Y,Z, by the following equation:

By substituting Y and Z, respectively, in thenumerator of similar equations, the chromaticitycoordinates for green (y) and blue (z) may alsobe calculated. Since the coordinates represent frac-tional values, then the sum of x, y, and z willalways equal unity, 1.0. The x, y values are plottedon the Chromaticity Diagram (see p. 18).Weighted functions used toreduce spectrophotometricdata to colorimetric terms(tristimulus values X,Y,Z).These functions define theBLUE "Standard Observer" tec-ommended for colorimetryby the lnternational Com-mission on lllumination -the 1931 C.l.E. standardobserver.

500 600WAVELENGTH (Na nometers)

\\rhen the chromaticity coordinate values for xand y are plotted on the C.I.E. ChromaticityDiagram, the intersection point will be a graphicpresentation of the chromaticity of the given color -in reiation to the three theoretical primary colorsof the diagram. Notice on the C.LE. diagram onthe foliowing page that the point of equal energy(white) is located at .333 on the x (red) axis, and.333 on the y (green) axis. The chromaticity pointsfor several fluorescent lamp colors are also shownon the C.I.E. diagram on the next page.

After the chromaticity point of a color has beenlocated on the C.I.E. Chromaticity Diagram, it isa simple matter to derive that color's dominantwavelength and purity. A line drawn from thepoint of equal energy - through the color's chro-maticity point - will intersect with the spectral energyIocus al tfu dominant wavelength. And since thespectral energy locus represents 100/o purity, andthe point of equal energy represents Oft purity,then the distance between the point of equal energyand the chromaticity point - as a ratio of the dis-tance between equal energ'y and the locus point -becomes the percentage of purity for the color to beidentified.The designation of a color on a C.I.E Chro-maticity Diagram gives no information on thespectral energy distribution of the light source orobject. (Even though the first inputs to the chro-maticity formula are the energy at each wave-length, they are concealed as soon as they areaveraged.) Therefore, identifying the percentagesof the primaries in a color is not a complete coloridentification system since many different combin-atiors of spectral energy mixtu-res can result in thesame apparent color.The present C.LE system is, however, moreaccurate than both the Ostwald and Mursellsystems because it specifies color on a physicalbasis - eliminating the need for human or sub-jective comparisons or judgments. The most com-plete measurement of color, then, would necessarilyhave to include the C.I.E. chromaticity, dominanthue, and purity data together with the spectralenergy distribution data in order to pinpoint allkey variables.COLOR TEMPERATUREAll objects will emit light if they are heated to asufficiently high temperature. Also, as an objectis raised in temperature, the color of the lightemitted from it will change. An iron bar, forexample, appears dull red when first heated, thenred-orange, then white, and finally blue-white as itis heated hotter and hotter. In the same way, atungsten filament in an incandescent lamp changescolor when different voltages are applied. Thisphenomenon was studied by Max Planck in 1900and is the basis for his law of blackbody radiators.This law, in essence, predicts the distribution of

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thermal radiation as a function of temperature,and defines the upper limit of thermal radiation.A blackbody is defined as one which will absorball radiation falling on it.This law can be used to designate the relativecolor temperature of any heated object. A colortemperature designation, applied to a light source,refers to the absolute temperature in degrees Kelvinof a theorectical blackbody or full radiator whosecolor appearance matches that of the source inquestion. Such a body is black at room temper-ature, red at 800K, yellow at 3000K, white at5000K, pale blue at 8000K, and brilliant blue at60,000K. Tungsten filament lamps used for generaiIighting have color temperatures in the 2600K to

3000K range. Low wattage iamps used where lumi-nance is not too important operate at about 2000K.Such lamps as TV and studio floods operate in the3100 - 3400K range, just short of the tungstenmelting point of 3500K. In most cases, actualfilament temperature is slightly lower than theapparent color temperature.

Technically, a "color temperature" designationcan only apply to incandescent sources, and, assuch, it is a specification of both the degree ofwhiteness and the spectral energy composition ofthe source. However, the term "apparent colortemperature" is often used to specify the degree ofwhiteness of fluorescent lamps as well as sky light,mercury vapor lamps, etc.


19/32

Typical exampies of "apparent color tempera-ture" values are as foliows:Warm White (WW) and Deluxe Warm White(WWX) Fluorescent Lamps 3000KCool White (CW) and Deluxe Cool White(CWX) Fluorescent Lamps 4200KWhite (W) Fluorescent Lamp 3500KDaylight (D) Fluorescent Lamp 7000KSunlight at sunrise 1800KSunlight at noon 5000KSky - overcast 6500KSky - extremely blue (clear northwest) 25,000K

A few of these lamps are shown together with theblackbody locus on the adjacent C.LE. Chromati-city Diagram.Unfortunately, the apparent color temperaturedesignation for any light source does not giveinJormation on its specific spectral energy distri-bution. For example, Cooi White and DeluxeCool White lamps appear to be the same colorbut their spectral distribution curves are quitedifferent and their effects on colored objects andmaterials are definitely different. The same limit-ation applies in using color temperature notationsto specify sky light, mercury vapor lamps, etc.


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STANDARD LIGHT SOURCESThree sources have been selected by the C.LE. as standardsfor use in colorimetry. These sources are designated sourceA, B, and C. Calibrated iamps may be obtained from theNational Bureau of Standards.

Source A is a tungsten filament lamp operating at 2854K.Source B utilizes a lamp having the spectral quality of sourceA in combination with a specified filter. The apparent colortemperature of source B approximates that of noon suniight(4870K). Source C is source A, the tungsten-fiiament source,but with a different filter. The filter and lamp combinationproduces a color quality which approximates daylight at6770K.

The adjacent chart gives the relative spectral energy distri-bution of these three standard light sources.RECORDING SPECTROPHOTOMETER

SPECTRAL ENERGYEMISSION, TRANS-MISSION, OR REFLEGTION OISTRIBUTIONCURVE

COLORIMETER @X BYx+2 CoMPUTATION v

c.t.E. srAr IDARD LIGHT S( )uRcEsSOURCE

"c"III-IIII ,iB.'..^ :,,/f: SOURCEr"/t'\i!-l ,,-,/ //

oE.UzUUFJUE

100

OL400 500 600WAVELENGTH (Nanometers)

COLOR MEASURING INSTRUMENTSThe two most common color measuringinstruments in use today are the spectro-photometer and the colorimeter. Their oper-ating principles are quite different, asillustrated on the adjacent diagrams.

The spectrophotometer gives the radiantenergy at each unit wavelength across theentire visible spectrum, while the colorimetergives only the sum of radiant energy foreach primary. Spectral energy data fromeither may be used to calculate the C.LE.chromaticity of a color, but it is obviousthat the spectrophotometer calculations willbe more accurate since the input data aremore complete.Spectral energy distribution curves fromspectrophotometers are often used for colormatching where high accuracy is essential.

Conversely, colorimeters are not as accurateas spectrophotometers over broad ranges, butthey are effective for general color matching -where minor color variations are immaterial.Colorimeters are quite accurate within narrowcolor ranges, though, and are often built intoproduction color control operatiors.Both devices will perform in either additiveor subtractive modes, and thus will providecolor measurements from similar light sourcesor object colors.


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o WHITE LIGHT SOURCESThe types of white light sources in use today varygreatly. Fluorescent, incandescent, and high inten-sity discharge lamps, as well as natural daylight areall thought of as sources of white light. But as wehave seen in previous sections of this book, whitelights are seldom what they seem - each varyingsignificantly from others in spectral energ'y content -and ali appearing white to the observer because ofthe synthesis function of the brain and psycho-logical adaptation variations.The goal of lamp designers has been to achievegood commercial sources of white light. The threecriteria or requirements are: 1) efficiency, or themost light per dollar, 2) color rendering, or theabiiity to make objects appear in their most familiarcolors, and 3) whiteness, or absence of color tints.Continual research and development with lightsource materials has produced remarkable improve-ments in today's light sources, but, as yet, theperfectly balanced lamp has not been achieved.The best of lamps available are the results ofcompromises among the three prime criteria. Themost efficient light sources known are deficient incolor rendering capabilities. To improve color ren-dering, filten and coatings must be added - butthey reduce the efficiency. And obtaining a lampthat "appears" white. can only be achieved byaffecting both efficiency and color rendition. How-ever, each type of light source has speciai ad-vantages which are useful and important in differenttypes of applications.

TYPES CIF LNGHT 5#1,!RCEsThere are three basic types of light sources usedtoday - incandescent, fluorescent, and high in-tensity discharge lamps. Incandescent lamps pro-duce light by electrically heating high-resistancetungsten filaments to intense brightness.

Fluorescent lamps produce light by establishingan arc between two electrodes in an atmosphereof very low pressure mercury vapor in a chamber(the glass tube). This low pressure discharge pro-duces ultraviolet radiation at wavelengths whichexcite crystals of phosphor (the white powder) liningthe tube wall. The phosphor fluoresces, convertingultraviolet energ'y into visible energy - light.Mercury, Multi-Vapor *, and Lucalox @ iampsare high intensity discharge t;.pes. They alsoproducelight by establishing an arc between two electrodesbut the electrodes are only a few inches apart - inopposite ends of a small, sealed, trarulucent ortransparent arc tube. An arc of electricity spanningthe gap between the electrodes generates heat andpressure much higher than in fluorescent lamps -high enough to vaporize the atoms of various metal-

* Trademark of the General Electric Company.

lic elements contained within the arc tube. Thisvaporization causes the atoms to emit large amountsof electromagnetic energy in the visible range.The metallic element in mercury lamp arc tubesis mercury. In Multi-Vapor lamps, small quantitiesof sodium, thallium, and indium iodides are addedto the basic mercury. In Lucalox lamps, sodium isthe primary element but a small amount of mer-cury is added.

Incandescent general lighting lamps produce from17 to 23 lumens''' of light per watt of power con-sumed - depending on wattage, life, and physicaldesign features. The bulk of the radiated energyfrom incandescent lamps lies in the invisible in-frared region of the spectrum (see chart on nextpage). Typical white fluorescent lamps produceabout 50 - 80 lumens per watt - depending ontheir size and type. Mercury lamps emit about 50-55 Ipw, Multi-Vapor lamps about 80 - 90 lpw,and Lucalox lamps, the most efficient of all, over100lpw.

INCANDESCENT LAMPS: (1 ) Pressed glass "PAR"(parabolic aluminized reflector) weatherproof spot or flood.(2) General purpose A-line. (3) Blown glass (reflector)spot or f lood. (4) 5OO-watt [email protected] rapid startline instant start.sta rt.

LAMPS: ('l ) Power Groove@ high(2) High output rapid start. (3) Slim-(4) Standard 40-watt pre-heat rapid

HIGH INTENSITY DISCHARGE LAMPS: (1) Multi-Vapor. (2) Phosphor-coated mercury. (3) Lucalox lamp." The lumen is the unit of luminous flux equal tothe flux in or unit solid angle from a uniformpoint source of one candela.


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CLEAR MERCURY DELUXE WHITE IIlERCURY

High intensity discharge lamps produce pealis ofenergy at specific wavelengths. These are deter-mined by specific shifts in electron orbits within theatomic structure of the metal. Thus, energy isemitted in "resonance lines" that are different foreach metal.For clear mercury lamps, major resonance radi-ation occurs at 405, 436, 546, and 578 nanometersin the visibie spectrum, and also at 253,296, and365 nanometers in the ultravioiet.(The outer bulb of the mercury lamp absorbsmost of the shortwave UV). Phosphor-coatings ap-plied to the inside of the bulb absorb this ultra-violet, and radiate energy with continuous char-acteristics to improve the color of the clear mercurylamp, as in the Deluxe White lamp illustrated.

The Multi-Vapor iamp also contains mercury'but severa] metallic iodides (e.g.' sodium, thaliiumand indium) have been added. The mercury reso-nance radiation is subordinate, and most of the

MULTI-VAPOR

SPECTRAL ENERGY DISTRIBUTIONA graphic presentation of the energy emitted by aIight source at each wavelength in the spectrum iscalled a spectral energy distribution (S.E.D.) curve'The S.E.D. data are derived through a spectro-radiometer, and are usually adjusted to some com-mon reference (such as output per lumen) to providea basis of comparison among sources. The curveson the adjacent chart represent such data for onephase of natural daylight and for many of the mostcommon general lighting sources.

Incandescent lamps obey established physical lawsof thermal emission; energy is distributed in asmooth curve beginning in the near UV range withvery little deep blue radiation, increasing withwave-length into the deep red. Elergy actually peaks inthe near infrared. Data are iho*n for color temper-atures common in general lighting lamps (3000K)and photoflood or studio lighting lamps (3400K).Because it has relatively more blue and less redenerg'y, the 3400K source appears much "whiter"than the slightly yeliowish general lighting lamps.

/5

50

2a

400 700 400WAVELENGTH (Nanometers)

DELUXECOOL WHITEFLUORESCENT

SOFT WHNATURAT ITE

22


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E:=5

ooc

light comes from the four lines (410,451,535, and590 nanometers) characteristic of the iodide addi-tives. The spacing of the lines and relative energyof each in the Multi-Vapor spectrum yields whiterIight and better color rendering than the clearmercury lamps.The Lucalox lamp is basically a sodium arc.Sodium's normal resonance radiation is at 589nanometers (actually, a "doublet" or two Iines at589 and 589.6, called the sodium "D" line). How-ever, the temperatures reached in the Lucaloxlamp's arc causes a remarkable reversal: The D-lineradiation is absorbed, and the energ"y is re-radiatedat shorter and longer wavelengths. This producesa relativeiy continuous S.E.D. curve with a dip at589 nanometers. A small amount of mercury is alsoin the arc tube, and traces of the mercury lines areradiated.In the fluorescent lamp, most of the arc radiationis at the 253.7 nanometer ultraviolet line, butphosphors selected for sersitivity to this UV lineabsorb and re-radiate the energy in various con-tinuous spectra as shown. In addition, there is asmall amount of radiation in the mercury resonanceIines.

COLOR EFFECTS OF WHITE LIGHT SOURCESSelecting a "white" light source on the basis of itscolor appearance or its color rendering" propertiesalone is rarely done for general lighting. Often,

* The term color rendering with reference to lightsources is a measure of the degree to which theperceived colors of objects illuminated by variouslight sources will match the perceived colors ofthe same object when illuminated by standard lightsources, for specified viewing conditions. (Theseconditions include an observer with normal colorvision who has adapted to the environment illumi-nated by each source in turn).

efficacy (lumen output per watt consumed) is amajor consideration. Ease of shielding and direc-tional control, as well as maintenance and. over-allsystem economics also must be considered.Incandescent lamps generally are considered tohave a slight edge over other }amps in color render-ing - not because they render colors more naturally,but because through decades of usage they havecome to be considered the norm. "Good" renditionis generally interpreted to mean the "familiar"appearance of familiar objects - and objects assume"familiar" colors only by being frequently seenunder certain types of light sources (daylight orincandescent). If fluorescent lamps had come intowide usage before incandescents, it is possible thatobject colors would appear most "familiar" underthem - instead of incandescents.Color and color rendition are as much functionsof individual preferences as they are functions oflight sources. People are familiar with the color

effects of daylight - which emphasizes cool colors,and equally familiar with the color effects of in-candescent lamps - which accentuate warm colors.This obviously incongruous situation is compoundedby the effects of memory, atmosphere, environment,and personal color preferences - to the point where"true colors" and "true color rendition" are verysubjective at best. The choice of which lamps to usefor which situations always wili vary according topersonal preferences. The color rendering propertiesof lamp types described on these pages may be ofconsiderable aid, however, in pointing out to lampusers the relatiue color effects of white light sources.Some lamps tend to "flatter" object colors -

which is another way of saying they emphasize thedominant color of the object while deemphasizingcomplementary colors. For example, Warm Whiteand Deluxe Warm White fiuorescents and ali in-candescent lamps will bring out warm object tones;

INCANDESCENT LAMPS


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the more efficient \'Varm \\rhite fluorescents lackthc capability to bring out reds, but do emphasizeother \\,arm toncs. The Deluxe \\''arm White isusually recommended for homes and other appli-cations r,vhere illumination u'ill be fairly lorv (50 fcor less) and the atmosphere u,ill be primarily "soc-ial. "On the other hand, u'hen a cooler atmosphereis desired, ,Deluxe White mercury, Multi-Vapor,and Cool White and Deluxe Cool White fluorescentlamps are most frequently used because they flatterthe cool colors. This results in a crisper atmospherer'vhich is usualiy related to higher illumination ormore serious activity, as in offices, schools, industrialplants and many stores. \\tith fluorescent, DeluxeCool White is recommcnded for areas ."vhere colorrendering is imporrant.N{ercury lamps are compietely satisfactory intheir rendering of blacks, whites, and grays, butthe scarcity of red and the concentration of blue,green, and yellow in a ferv narro\\r bands makesthem poor sources for producing the familiarappearances of warm colors. Ilowever, recent years

have seen improved color mercury lamps achievedby the addition of phosphor coatings. The mostsignificant of these has been the Deluxe \{hitephosphor, which yields color rendering fully asacceptable as that of Cool \Vhite, the most rvidelyused fluorescent color.The Lucalox lamp produces a sunny atmospherewhere used - because of its greater amount ofyellow and orange energy, and reduced blue. Al-though the current Lucalox lamp, like the Muiti-Vapor iamp, is most frequently used where colorrendering is secondary to efficacy, its pleasantgolden-white color offers many new applicationopportunities for this powerful nerv light source.Prospects are promising for Lucalox lamps of muchbetter color renderins capability.

The table plesented below is intended as a generalguide to lamp selection - giving a few indicationsas to the color effects of the lamps on atmosphere,people, and ob.jects.

LAMP SE oLFLUORESCENT LAMPS

Lamp Names Cool+White Deluxe*Cool White Warm*White Deluxe*+Warm White Daylight White SoftWhite/NaiuralEfficacy(Lumenslwatt) Hieh Medium Hich Medium Medium-High High MediumLamp appear-ance effect onneutral surfaces Whiie White

Yellowishwhite Yellowishwhite Bluishwhite Pale yellowishwhite Purplishwhite

Effect on"atmosphere"Neutral tomoderatelycool

Neutral tomoderatelycool Warm Warm Very Cool Moderatelywarm WarmprnKrsnColorsstrengthened Orange,Yellow. Blue All nearlyequal Orange,Yellow Red, OrangeYellow, Green Green. Blue Orange,Yellow Red, Orange

Colors greyed Red Noneappreciably Red. GreenBlue Blue Red, Orange Red, Green,Blue Green, BlueEffect oncomplexions Pale Pink Most natural Sallow Ruddy Greyed Pale Ruddy Pink

RemarksBlends withnatural day-Iight-Goodcolor accept-ance

Best overallcolor rendi-tion:simulatesnatural day-light

BIends withinca nd escentlight-poorcolor accept-ance

Good colorrendition;simulatesinca ndescentlightUsuallyreplaceablewith CW

Usuallyreplacea bl ewith CW orTinted Sou rceUsuallyre placea blewith CWX orWWX o

* Greater preference qt higher levels. ** Greater preference at lower levels.


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700 400 500 600WAVELENGTH (Nanometers)

500 600 700 400WAVELENGTH (Nanometers)

700

How light source affectscolor appearance, Theillustrations show howSED's of Cool White andDeluxe Cool White lampsare modified by reflec-tance of typical humancomplexion. Under thedeluxe lamp, much morered is reflected to theeye. Besult: A health-ier, more natural appear-ance. This is true thoughCW and CWX lampshave approximately thesame whiteness. De-luxe Warm White, whichde-emphasizes bluessomewhat, is even moref lattering to complex-i ons.-

OCT roN GUIDEINCANDESCENT HIGH INTENSITY DISCHARGE LAMPS

otUzUUFJUE

REFLECTED LIGHT

(5tUzUUFJUE

REFLECTED LIGHT

Lamp Names Filament+* ClearMercury WhiteMercury Deluxe Whiie*Mercury Multi-Vapor* Lucalor* +Efficacy(Lumens/watt) Low Medium Medium Medium High H ighLamp appear-ance effect onneutral surfaces

Yellowishwhite Gree nishblue-white Greenishwhite Pu rpl i shwhite Greenishwhite Yellowish

Effect on"atmosphere" Warm Very cool,G reen is h Moderatelycool,Greenish Warm,Pu rplis h Moderatelycool. G ree n is h Warm,YellowishColorsstrengthened RedOrange

YellowYellowGreenBl ue

YellowGreenBl ue

RedYellowBlue

YellowGreenBlue

YellowOra ngeG reen

Colors greyed Blue Red, Orange Red, Orange Green Red Red, BlueEffect oncornplexions R uddiest Greenish Very pale Ruddy Greyed Yellowish

O RemarksGoodcolorrende ri ng

Very poorcolorrenderingModeratecolorrendering

Coloracce pta ncesimilar toCWfl uorescent

Coloraccepta ncesimilar toCWfluorescent

Coloracce pta rcea pproacfresthat of WWfl uorescent


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The second part of the Color Rendering Indexconcept is establishing a comparisoz between a givenlight source and the reference light source - anddenoting this comparison by an R factor, which isa ratio or percentage of how closely a given lightsource matches the color rendering ability of thereference light sources. The index for the R factoris based upon an arbitrary scale which places aspecific Warm White fluorescent lamp at R=50,and the reference source at R=100. The referencesource always has an R=100 since it means (theo-retically) that it is the reference standard for eachcolor point.EXAMPLES - The industry standard ColorRendering Index denotation for a specific warmwhite fluorescent lamp is R:50 at 3000K. ColorRendering Indexes are listed below for some of themore popular current General Electric fluorescentlamps.

COLOR RENDERING INDEXThe interpretation of the color rendering abilities ofIight sources has not been widely agreed upon inthe illumination industry, and the resulting con-fusion among lamp users is understandably great.Additional confusion has been generated by claimsof lamps which are said to duplicate sunlight, day-light or some other arbitrary comparison source' In1965, an industry standard was adopted as a steptoward establishing a uniform basis for determiningthe color rendering abilities of all light sources. Thisrating system is called the Color Rendering Index.

INDEX CONCEPT - The Color RenderingIndex is a two-part concept. The first part estab-Iishes the real or apparent color temperature of agiven light source on the CIE chromaticity dia-gram. If the color temperature of the given sourceis 5000K or less, then the reference or comparisonsource is that Planckian radiator of the nearestcolor temperature - or, if the color temperature ofthe given source is above 5000K, then the referencesource is the nearest reconstituted daylight source.(Reconstituted daylight represents a series of mathe-matically derived curves representing the weightedaverage of daylight at a given color temperaturemeasured at difTerent locations, elevations, times,etc.) These Planckian radiators and recorstituteddaylight curves then become the standard lightsources against which to compare any given lightsources.

Apparent GolorLamp Golor Name Color RenderingTemperature lndexWarm WhiteDeluxe Warm WhiteWhiteCool WhiteDeluxe Cool WhiteSign WhiteDaylightMETHOD - Determining the Color RenderingIndex, R, for any given light source requires pre-cise spectroradiomeffic data. The spectral distri-bution curve must be determined for the givenlight source and its apparent color temperaturecalculated. In the approved method, eight arbitrarystandard color samples are used and their apparentchromaticities - under the reference source - arecalculated. A similar set of calculatiors under thegiven light source - will produce eight differentapparent chromaticities. The differences betweenthese two sets of data indicate the "color shift" ofthe given light sources in relation to the referencesource. The final calculation results are then auer-

aged to arrive at the Color Rendering Index, R'INDEX LIMITATIONS - There are shortcom-ings in the Color Rendering Index rating whichmust be recognized to prevent its misuse. It will benoted in the calculation of R that each light sourcehas a specific color temperature reference. There-fore, two light sources cannot be compared unlesstheir reference is similar (within 100K to 300K ofeach other - depending on their location on thecolor temperature scale).AIso, it is important to note that two lamps mayhave the same ref.erence source and Color RenderingIndex - and still have drastic differences in theirability to render one or all colored materials iden-

3000K2900K3500K4200K4200K5200K7000K

R:52R:73R:60R:66R:89R:86R:79


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tically - because the R is an aaerage of the colorrendering ol eight or more specific colors - andbetter performance in some areas may be concealedin the average with poorer performance in otherareas.If the R is less than 90, these comparisons can beof questionable value since the direction of the colorshift has been eliminated, and tlne degree of shift insome areas may be quite different for differentsources.Finaily, it must be remembered that the ColorRendering Index is based upon arbitrary references(the Planckian radiator or reconstituted daylight).This choice is merely for convenience - and doesnol imply that the reference source is tine perfectcolor rendering source.INDEX ADVANTAGES - The Index will pro-vide sufficiently meaningful information on thecolor rendering capabilities of lamps to be of sig-nificant value to the lamp industry and to users -providing that all of the restrictions mentioned

above are adhered to.COLOR MATCHING AND GRADINGColor matching is, as the term implies, a processby which fabrics or other colored materials arematched with other fabrics or with completelydifferent materials. It is usually desirable to matchsuch materials under lighting conditions identicalto those under which the products are to be usedor displayed.

Color matching is done in various ways. Anartist may begin with a pure pigment colorant,adding white, black, or other colors. A printer,on the other hand, may alter the size of the half-tone dots to change the ink color tone in whichthe picture is printed, or add an additional dotpattern (screen) in a different color to change thefinal color.

Color grading and color shading are processes bywhich materials are divided into groups of colors

or tints or shades. For example, batches of whitechinaware in the process of being baked in a kilnmay vary slightly in whiteness. A trained colorshader can separate the products into several dozendifferent shades of white. This is important in theceramics industry since complete table settings mustbe well matched.Some objects may appear to be the same colorsunder a certain light source - and even have iden-tical C.I.E. chromaticity specifications - while theyare actually different in spectral composition. Thesecolors are called metameric. If the light source ischanged, however, the object color differences be-come readily apparent. Only color samples whichhave identical S.E.D. curves will continue to matchunder all light sources. The chart below illustratesthe phenomenon of metamerism. Color matchingof metameric colors also depends on the eyes of theviewer, since people differ considerably in the waythey see colors which are complicated in this man-

ner. The comparison and interpretation of thecurves of metameric colors constitutes a complexphase of colorimetry.In the past the "ideal" light sources for colormatching were thought to be the sun and sky,particularly because of their presumed color con-stancy. Actually, sunlight varies from about 1800Kat sunrise to 5300K at noon. Sky light ranges from7000K (uniform overcast) to 28000K for an ex-tremely blue clear northwest sky. Because of thesevariatiors, sky light and sunlight are not the bestof color matching sources.When the exact light under which materials areto be seen is not known, or when the materials aresuspected of being metameric, tao light sources ofwidej dlflerent spectral character should be used -one at a time - to examine the samples. One ofthe two sources used should be predominantiy bluein its spectral characteristics, such as daylight fluo-rescent lamp; the other should be predominantlyred such as a tungsten filament lamp.

Eooo-UJOz.FUJLUE.

METAMERISM - Chart at left shows absolute spectral reflectance of two metamericSpectroreflectometer). The same samples under tungsten filament iamps (center chart)Under Daylight fluorescent lamps (chart at right), they exhibit noticeable mis-match of color.wool samples (measured byappear to be the same color.


28/32

Color Booth - The color of an ob-ject is the result of the spectralcharacteristics of the light source,the reflectance characteristics of thematerial, and the level of illumina-tion used, A color booth whichprovides many different light sourcecolors and varying levels of illumina-tion can duplicate a proposed envi-ronment-and provide a dependablearea for color selection. Colorschemes should be selected underconditions duplicating those underwhich they will be used-to preventunexpected color shifts or mis-matches of color in actual use.

There are a few. materials that fluoresce, or pro-duce visible light, when irradiated by ultravioletenergy. For this reason, one inspection light sourcethat is predominantly blue should be used - es-pecially one that also contains enough ultravioletradiation so that these fluorescent effects can beproduced. The second light source - predominantlyred - should not emit ultraviolet energy.If it is not feasible to use two light sources forsome particular color matching job, the best sin-

gle source available today is the Deluxe Cool Whitefluorescent lamp, as this lamp has relatively bal-anced amount of energy in all portions of thespectrum. This means that all colors receive aboutthe same treatment, without undue emphasis onany one portion of the visible spectrum.If the color matching is confined to a particularcolor, as might be the case for a manufacturer ofblue denim textiles, the best single source underthese conditions is one that is essentially comple-mentary in coior to that of the product. For theblue denim, incandescent iamps would allow thecolor matcher to see more subtle differences incolor than would be the case with most other typesof illuminants.

For color-discrimination work where the gradercarries thc standard in his head, so to speak, it ismost important that the illuminant match as closelyas possible the source under which the grader wastrained, and to which he is accustomed. He remem-bers his standard samples as he saw them under a

particular illuminant. However, if it is not possibieto train the grader, then the best source is theDeluxe Cool White fluorescent lamp.For most types of color matching, 200 to 400footcandles are probably adequate. When dealingwith very dark colors, more than 1000 footcandlesare desirable.Color matching booths provide a controlled en-vironment necessary for critical inspection of manyobjects. The interior should be matte finished in

neutral tones - gray or white for objects havingdiffuse surfaces, black for those with specular orpolished surfaces. Matte black eliminates maskingreflections that would obscure the true color of theunderiying pigment. In all cases, the neutral toneshave little or no influence on the color of the ob-j ect.In addition to being graded for color, fabricshaving shiny surfaces are inspected for uniformityand amount of sheen. For this purpose, the lightsource should be of high luminance, and should becarefully positioned so as to reveal any variation inthe specularity of the material.

For critical color grading and matching, it isdesirable to position the light source in such a man-ner that reflections of the source are directed awayfrom the irspector. With three-dimensionai objects,however, elimination of all refiected images of thesource may not be possible. Therefore, a luminairerelatively large in area and uniform in brightnessis the best choice for this application.


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GOLORED LIGHTSOURGESThe colon of light are commonly described in terms of hue.saturation, and brightness. Hue refers to the quality that can bedescribed as red, green, etc. In everyday language, the wordcolor is often used to mean hue. In the C.I.E. color system, it isthe dominant wavelength. Saturation, like N{ursell's Chroma,and C.I.E. purity, refers to the amount by which the lightappears to differ from white - the strength or depth of thecolor. A deep red light, for example, is said to be of highsaturation. Brightness is related to the apparent quantity oflight, without regard to hue or saturation.Most colored light sources, even those that appear highlysaturated, are not truly monochromatic - that is, they emit afairly wide band of wavelengths, often including small amountsof energy in other hue regions. The less saturated the color,the greater the content of other hues. (See adjacent spectralenerg'y distribution charts.)Yellow light is unusual in that a strong sersation of yellow'may be produced either by monochromatic light of about 580-600-nanometer wavelength, or by mixture of red and greenlight covering about two-thirds of the spectrum (see adjacentspectral chart of yellow lamps). In fact, it is theoretically possi-ble to have a light that appears yellow, but contains no energyat the wavelengths normally seen as yellow. (However, there areno practical iight sources of this type.)HOW LAMP COLORS ARE CHANGEDColored light can be produced by starting with white light andfiltering out or subtracting the undesired portion of the spectrum.A colored or filtered incandescent lamp uses this principle. Orcolored light can be produced by a light source which generatesonly the desired portion of the spectrum - such as fluorescentlamps in which variations in phosphor produce varying colors ofIight.

So-called natural colored incandescent lamps have bulbs oftransparent colored glass. But the bulbs of most colored sign anddecorative lamps begin as clear glass; then are coated with finelyground colored glass (vitreous glass enamel); and finally, they arefired to fuse the coating into a hard, colored enamel finish. Thecoatings contain a white pigment, as well as colored ones, forbetter diffusion of light. The tinted Coloramic@ Iamps aremade in a similar manner.Lexan@ color sign lamps have a transparent polycarbonateresin plastic coating. They offer more sparkle, greater brightness,and higher saturation for any given coior. For instance, the blueand green Lexan-coated lamps are freer of red, and have a moredistinct separation from each other. For this reason, the contrastsbetween warm and cool colon are also greater, such as betweenred and btrue.Colored reflector lamps (R-40's and R-30's) also have firedenamel finishes. But these colored glass coatings contain no extradiffusing material - to preserve the transparency so the light

YEtL0W t-40

WAVETENGTH (tronom.l.r)

WAVIL:NCIH {fl onon.r.tr)

llo aoowAvllCNGlH (Nonomrtrn)

BtuE t.40IILAMTNT8I.U E

REO r-40FITATENT


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beam will not be broader than desired. The100-watt PAR-38 lamps have a coating of dye-impregnated silicone plastic, similar to the Lexan-coated lamps. There are 150-watt PAR-38 red,amber, and yellow lamps with stained glass faces.In this case, a coloring material is applied to oneside of the glass. The glass is then baked, causingthe color to stain a thin layer of the cover plate.Interference filters involve one or more very thinlayers of selected materials deposited (in a vacuumchamber by evaporation techniques) as a film on abase material such as clear glass. The thickness ofeach layer is usually less than one wavelength ofIight. The filters make use of the optical principleof interference to pass a limited band of wave-lengths. The center wavelength and spread of thetransmitted band are determined largely by thethickness and number of layers in the film. How-ever, unlike other filters, the wavelengths not trans-mitted are reflected, as from a mirror, rather thanabsorbed. Therefore, these filters stay relativelycool.

COLORED FILAMENT LAMPS: Repre-sentative sign, floodlighting, decorative,and display lamps.Broad-band interference filters are often calleddichroic (two-colored) because they transmit onepart of the spectrum and refiect the other. SomePAR lamps make use of these filters - Cooi-BeamIamps that separate much of the visible from theinfrared wavelengths; and Dichro-Color lampsthat use the interference principle to produce a fullrange of saturated colors.Fluorescent lamps produce colored light by theuse of special phosphors. These interior coatingsconvert the ultraviolet energy generated within thelamp to visible light of the desired wavelengths. Intwo colors (Deep BIue, and Red), colored filteringmaterials are added to the outside bulb wall toproduce more saturated colors than can be pro-duced by the phosphors. The gold fluorescent lamp,however, achieves its color by subtraction - sinceno phosphors emit primarily yellow light. A yeliow

COLORED FLUORESCENT LAMPS:Reading left to right*green. deep blue,gold. pink, blue, and red.filter coating on the inside of the tube absorbs theunwanted wavelengths from a warm white phos-phor.

Blacklight (BL) fluorescent lamps utilize a specialphosphor that emits primarily near-ultraviolet ener-gy with a small amount of visible blue light. Butfor many BL effects, even a small amount ofvisible Iight is undesirable. For these situations,BLB lamps - made of a special dark filter glass -transmit the near UV energy but absorb virtualiyall of the visible energy.EFFIEAEY OF EOTORED I-IGI.IT SOURCESLuminous efficacy is reduced whenever subtractive(filtering) techniques are used. To obtain any strongcolor with filament lamps, it is necessary to removemost of the light emitted by the filament. The moresaturated the color, the lower the efficacy of thesource-plus-filter combinations. Because it is nec-essary to remove the greatest amount of energyto obtain the correct hue, cool color iamps, such asblue, .have the lowest efficacy of filament types.In the case of fluorescent lamps, the phosphors areusually selected to generate the desired hue - asubstantially more efficient process.

The following table shows a comparison of theefficacy of fluorescent and filtered filament lampsproducing colored light of approximately the samesaturation.Efficacy of Fluorescent and

Filtered Filament Lamps ProducingGolored light of Approximately the Same Saturation

O-watt Fluorescent Filament*(Lumens per watt) (Lumens per watt)redpinkyellowgreendeep bluebluelight blue

52A55100112863 (Daylight color)

2-36-8to-L2r.5-2.5L-24-6

* Uncolored lamp assumed to be 16 lumens per watt


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ADDITIOI\IAL REFE RENCESTP-l28 FOOTCANDLES IN MODERN LIGHTING.TP-117 TEXTILE LIGHTING ,TP-120 HOME LIGHTING BULB GUIDE.TP.'I 02 SCHOOL LIGHTING.TP-106 STORE LIGHTINGTP- 1 08 INDUSTRIAL LIGHTINGTP-114 OFFICE LIGHTINGTP-109 MERCURY LAMPS .TP-1 1O INCANDESCENT LAMPS .TP-1 1 1 FLUORESCENT LAMPS

OTHER GE PUBLICATIONSRELATED TO LIGHT AND COLOR

TP-118 LIGHT MEASUREMENT AND CON.TROL. Contains detailed information on port-able and laboratory light measurement instru-ments, and techniques for measuring lumenoutput and brightness. Expanded explanationsfor object surface effects on light waves. suchas reflections, transmission, etc. (28 pages.)

TP-129 LIGHT AND INTERIOR FINJISHES.Itemizes the considerations of ref lectance,visual comfort, lighting efficiency, atmosphere,surface color, and light source color in de-signing products and living spaces. lncludescolored reflectance sample chips. (8 pages.)TP.121-R SUPPLEMENTARY LIGHTING.Presents the needs and benefits of supple-mentary lighting to ease difficult seeing situ-ations in industry. Special discussions on colormatching and grading, size and brightness ofsupplementary light sources, and speciallamps and techniques. (1 6 pages.)

TP-101 GENERAL LIGHTING DESIGN. Con-tain basic information about the lumen methodof general lighting design. Booklet includestables for footcandle levels, room ratios,coefficients of utilization on luminaires. aswell as lighting comfort design data.(1 6 pages.)

20 pages1 6 pages1 6 pages1 6 pages24 pages2O pages24 pages1 6 pages32 pages24 pages


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GENERAL ELECTRICLAMP SALES DISTRICTS AND DISTRIBUTION CENTERS

Ciry

SALES DISTRICTS(To Obtain Sales and Technical Inlormation)Addres6 ZIP Area TelephoneNo. Code No.

DISTRIBUTION CENTERS(To Order Lamps and to Obtain Shipping lnformation.Local Warehouse Stocks maintained at these Points)

zlPNo.ddress Area TelephoneCode No.

N.Y.

MD. ,,,,,.MASS.N.Y. ,,,.,,,,N.C. ..,.,tLL. .. . ..... .oHro .....

OHIO ,,.,TEXAS ,,,,,,.COLO. .......

TEXAS ,,,,.IND. - ,.MO. ..,,CALIF. ,

TENN. ..,,,,FLA. WtS. .....MINN. ,,

N.J. ., , ,.... .HAVEN, CONN. ...LA .., ,YOFK, N.Y. .,,,...YORK, N.Y, ..,,,,.CALIF. ,,,,.

PA. ,,,,PA. ..,,,

ORE. , ,.,, ,VA. ,,,....LAKE CITY, UTAHWASH. ,,...,

LOU|S, MO. ........

D.C. ....

4 Avis Drive, Latham, N.Y. .........120 Ottley Drive, N.E. ....... P.o. eo" i+SziComme,cral & lndust. alConsumer Producls .1401 Parker Road ..... ....... P,O. Box742750 lnduslrial Place- P,O, Box 257.Newton Upper Falls. Mass.770 Riveruiew Blvd., Tonawa.da, N.Y. .......1001 Tuckaseegee Rd. ........... P.O. Box 341444333 Trans World Rd., Schiller Park, lll. .., ...Kenwood Professional Bldg9403 Kenwood Road......Commercial & lndustrial .Consumer Products ....'1705 Noble Rd......,,.... P.O. Box 2494Commercial & lndJstnalConsumer Products .6500 Cedar Springs Rd. ...... P.O. Box 354256501 Stapleton Drve, North1 5135 Hamilto" Avenue . . .1200 Blarock Road, Su,te 210...... .... . .. . .251 1 E. 46lh Slreet. Suile P . . P,O, Box 55650Commercral & lndust'alConsuner Products .535 East 14th Ave,, N. Kansas City, Mo. .....

1 21 1 0 (51 8) 783-61 8818930376 (404) 897-2872(404) 897-285021227 (301) 242-570002164 1617) 332-620014150 (716) 874-518028208 (704) 376-658528234 (704) 376-658560176 (s12) 671-639045242 (513) 745-5730(513) 745-573344112

(21 6) 266-4256(216) 266-426475235 (214) 358-53218021 6 (303) 320-359748203 (313) 956-020077055 (713) 932-647246205 (317) 547"55131141317) 547-551111264116 (816) 471-012s90040 (213) 725-2677381 09 (901) 774-9016(901) 774-901533147 (305) 693-381153201 (414) 462-s8605542455440 (612) 535-515107932 966-5400966"5400932-2274

733-9200

14150 (716) 874-518030376 (404) 897-2800Buffalo Distr. Ctr., 770 Riverview Blvd., Tonawanda, N.Y. ........120 Otiley Drive, N.E. ..... P.O. Box 14529

6500 Cedar Springs Rd. ... P.O. Box 35425 75235 (214) 358-53216501 Stapeton Drive, North 80216 (303) 320-359715135 Hamilton Avenue .. 48203 (313) 956-02007402NeuhalsAve........ P,O,Box1291177017 1713) 644-3264Cincinnati D str. Ctr., 49 Central Ave., Cincinnati, Ohio . ......... 45202 (513) 559-3600

1401 Parker Road.. -..50 lndustrial Place- P.O. Box 257,Newton Upper Falls, Mass. .........770 Riverview Blvd., Tonawanda, N,Y1001 Tuckaseegee Rd..............4201 Souih Pulaski Road49 Central Avenue . . .

1705 Noble Rd. ,,......

535 East 1 4th Ave,, N. Kansas City, Mo2747 Soulh Malt Avel-e2021 South Latham Slreet3655 N.W. 71st St. . . ...8100 West Florist Ave. 53218 .......8501 54th Avenue, ^,1o. ........ ......133 Boyd St'eet

26-45 Brooklyn Queens Expway, Woodside, N.Y999- 98th Avenue 94603.'1000 Continental Rd.-P.O. Box 299,Krng ol Prussia. Pa. .......575 Epsilon Dr. .. ...

P.O.Box7427 21227 (301) 242-5700.... 02164 (617) 332-6200.... 14150 (716) 874-5180P.O.Box34144 28234 (7O4) 376-6585.... 60632 (312) 254-6161.... 45202 (513) 559-3600

P.O.Box2422 44112 (216) 266-4404

..., 64116 (816) 471-0123P.O. Box 22078 9oo4o (213J 725-2677

.... 38109 (901) 774-9045. . P.O. Box 470A57 33147 (305) 693-381 1..... P.O. Box 299 53201 (414) 462-3860.....P.O. Box 1278 55440 (612) 535-5151. . . . . . P.O. Box 439 071 01 (201 ) 622-8000

11227 (212J 896-600070181 (504) 733-920011227 (212) 856-600011377 (212) 896-6000P.O.Box24354 94623 (415) 436-9433

.... 19406 (215) 964-2900P.O. Box 2801 15230 (412) 963-9141

3655 N.W. 71st St....,.,.... P.O. Box 4708578100 West Florlst Ave. 53218... P.O. Box 2998501 54lh Avenue, No., New Hope, M nn. ......,, P.O. Box 12786 V/eeland Road, Florham Park. N.J. .........Commercral & lndust4alConsumer Products .145 Ora^ge Ave.. West Haven. Conr. ........701 Edward Ave,, Harahan, LA ..............lvla'l: P.O, Box 10236, Jelfe'son, Lou'siana ...2'5 Lexington Avenue ..Commercial & lndustflalConsumer Products .26-45 Brooklyn Queens Expway, Woodside, N.Y.999-98th Avenue 94603 .... P.O. Box 24354Commercral & lndusF'alConsuner ?roducts'|.000 Continental Drive-P.O. Box 299.King of Prussia, Pa. ........600 N. Bell Avenue, Carnegiei"rr","i"i a i.or.ila ...Consumer Products .....,4930 Third Ave. So. ...,....Commercial & lndustrial ...

2747 South Malt Avenue ...201 1 S. Latham St. .... . . ..Commercial & lndustrial ..Consumer Products .....

Consumer Producls ..........1401 Parker Rd.-P.O. gox7427.Baltimore, Ny'd..

P.O. Box 9335

(201 )(201 )06s16 (203)7012370181 (504)'10016 (212) 750-3028(212) 750-2180113V7 (212) 896-600094623 (415) 436-9450(41 5) 436-9470

..,. 19406 (215) 964-2900Pa............ 15106. P.O. Box 2a32 15230 (412) 566-4300(412) 566"4307. P.O. Box 3877 98124

N.Y. Distr. Ctr., 75-11 Woodhaven Blvd,, Glendale N.YMail: P.O. Box '0236, Jelfe'son, LA ................75-11 Woodhaven Boulevard, Glendale, N.Y. ........

Portland Distr. Ctr., 2800 N. W. Nela Street..... P.O. Box 10006 97210 (503) 221-5120Consumer Products ...2015 Staples N,1ill Rd., Room 425 ............1605 Empire Rd. 84104 ...... P.O. Box 265484930 Third Avenue South ..... P.O. Box 3877Conmercral & lndustr'alConsumer Producls .'1530 FarNrew Ave"ue .........100 Elwood Davis Boad, N. Syracuse, N.Y. ...

11 101 North 46th S1. 33617... P.O. Box 16626Commerc al & lndLst.ial

(206) 292-7914(206) 292-683823230 (804) 355-328984125 (801) 974-451198124 (206) 292-7914(206) 292-683863132 (314) 997-841313212 (315) 456-297533687 (81 3) 988-7351(813) 988-7351Ext.37138(813) 988-7351..... 21227 (sO1) 864-6105

Baltimore Distr. Ctr,-P.O. Box 7427, Baltimore,Md. ..........., 212271605 Empire Rd., Mail: P.O. Box 26548 .... 441254930 Third Avenue South .. P.O. Box 3877 98124lS30 Falruiew Avenue ........ ........ 63132Buflalo Dist. Clr., 770 Rlverview Blvd., Tonawanda, N.Y. ........ 1415011101 Nodh 46th St. 33617. ......... P.O. Box 16626 33687

(301) 242-5700(801) 974-4505(206) 292-7891(31 4) 997.841 3(716) 874-5180(813) 988-7351Ext. 37138

Baltimore Distr. Ctr.. 1401 Parker Rd P.O.8ox7427 21227 (301) 242-5700ln addition to the Sales Disilict Headquarters cities listed above, GE Lamp Sales Representatives are residentin 100 other cities. Consult your telephone directory under General Electric Company Lighting Business Group,

GENERAL ELECTRIC COMPANYLIGHTING BUSINESS GROUPGENERAL OFFICES: NELA PARK, CLEVELAND, OHIO 441 1 2

GENERAL@ETECTRtC

Documents

GE Light & Color Brochure 1978