PHOSPHOR
`HANDBOOK
`
`Edited by
`Shigeo Shionoya
`William M. Yen
`
`NICHIA EX2019
`
`

`

`PHOSPHOR
`HANDBOOK
`
`Edited under the Auspices of
`Phosphor Research Society
`
`Editorial Committee Co-chairs
`Shigeo Shionoya
`William M. Yen
`
`Members
`Takashi Hase
`Shigeru Kamiya
`Eiichiro Nakazawa
`Kazuo Narita
`Katsutoshi Ohno
`Masaaki Tamatani
`Marvin J. Weber
`Hajime Yamamoto
`
`(g)
`
`CRC Press
`Boca Raton Boston London New York Washington, D.C.
`
`I1
`
`NICHIA EX2019
`
`

`

`Acquiring Editor:
`Project Editor:
`Cover design:
`
`Robert Stem
`Albert W. Starkweather, Jr.
`Dawn Boyd
`
`Library of Congress Cataloging-in-Publication Data
`
`Phosphor handbook / edited under the auspices of the Phosphor Research Society ; editorial committee co-
`chairs Shigeo Shionoya, William M. Yen ; members Takashi Hase ... [et al.]
`p. cm.
`Includes bibliographical references and index.
`ISBN 0-8493-7560-6 (alk. paper)
`1. Phosphors-Handbooks, manuals, etc. 2. Phosphors-Industrial applications-Handbooks, manuals,
`etc. I. Phosphor Research Society.
`QC476.7.P48 1998
`620.11295—dc21
`
`98-15663
`CIP
`
`This book contains information obtained from authentic and highly regarded sources. Reprinted material is
`quoted with permission, and sources are indicated. A wide variety of references are listed. Reasonable efforts
`have been made to publish reliable data and information, but the author and the publisher cannot assume
`responsibility for the validity of all materials or for the consequences of their use.
`Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic
`or mechanical, including photocopying, microfilming, and recording, or by any information storage or retrieval
`system, without prior permission in writing from the publisher.
`The consent of CRC Press LLC does not extend to copying for general distribution, for promotion, for creating
`new works, or for resale. Specific permission must be obtained in writing from CRC Press LLC for such copying.
`Direct all inquiries to CRC Press LLC, 2000 Corporate Blvd., N.W., Boca Raton, FL 33431.
`
`Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are only
`used for identification and explanation, without intent to infringe.
`
`© 1999 by CRC Press LLC (English language version)
`
`© 1987 by the Phosphor Research Society (Keikotai Dogakkai) (Japanese language version)
`
`Originally published in Japanese by Ohmsha, Ltd. under the title Keikotai Handobukku.
`
`No claim to original U.S. Government works
`International Standard Book Number 0-8493-7560-6
`Library of Congress Card Number 98-15663
`Printed in the United States of America 1 2 3 4 5 6 7 8 90
`Printed on acid-free paper
`
`Pre)
`
`This vol
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`was org
`issued t
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`in the t
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`inphos
`opmen
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`NICHIA EX2019
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`

`

`f
`
`chapter five — section two
`
`Phosphors for lamps
`
`Shigeru Kamiya
`
`Contents
`5.2 Classification of fluorescent lamps by chromaticity and color rendering
`properties
`References
`
`367
`373
`
`5.2 Classification of fluorescent lamps by chromaticity and
`color rendering properties
`There are many kinds of fluorescent lamps of different chromaticities and different color
`rendering properties. According to the appropriate or particular application, lamps with
`suitable color chromaticity and color rendering can be chosen. In Japan, the classification
`of fluorescent lamps for general lighting is described in the /IS Standard Z92221 in accor(cid:173)
`dance with the chromaticity and color rendering properties.
`
`Classification by light source color. The described chromaticity ranges of five different
`colors in JIS are shown in Figure 2, together with the IEC specification. Designations and
`symbols of these five colors are shown in Table 3 as compared with those commonly used
`outside Japan. The 5000-K lamp is exceptionally popular in Japan.
`
`Classification by color rendering properties. Various kinds of descriptive wording are
`used by manufacturers to describe the degree of improvement in the color rendering of
`their lamps; words such as Deluxe type. Super Deluxe type, Natural Color, etc. are com(cid:173)
`monly encountered. /IS first introduced a standard designation system according to the
`color rendering indices and characteristics of the spectral power distribution.
`Fluorescent lamps with wide band spectra are classified into four types: ordinary type,
`color rendering A type, color rendering AA type, and color rendering AAA type, depend(cid:173)
`ing on the degree of improvement of the color rendering indices. The minimum required
`values of the general color rendering index and special color rendering indices of the lamp
`belonging to each category are given in Table 4. For narrow band fluorescent lamps, in
`addition to the requirement for color rendering indices, the ratio of the radiant flux within
`the three specified band wavelength regions to that in the entire visible wavelength region
`are specified. The symbol for narrow band lamps satisfying the values described in Table 5
`is designated as EX.
`
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`

`Figure 2 Chromaticity range of light source colors of fluorescent lamps (From JIS Standard Z 9112
`1990 With permission)
`
`Table 3 Chromaticity Range of Light Source Colors of Fluorescent Lamps
`JIS 9112
`
`Classification
`
`Symbol
`
`Daylight
`Day white
`White
`Warm white
`Incandescent color
`
`D
`N
`W
`WW
`L
`
`T
`(K)
`
`5700-7100
`4600-5400
`3900-4500
`3200-3700
`2600-3150
`
`IEC Publ
`
`81
`
`Daylight
`
`(D)
`
`Cool white
`White
`Warm white
`
`(CW)
`(W)
`(WW)
`
`Note Correlated color temperature T values are informative reference
`From JIS Standard Z 9112 1990 With permission
`
`Fluorescent lamps with wide emission bands Ordinary fluorescent lamps employ cal(cid:173)
`cium halophosphate phosphors, which have a broad continuous spectra Emission inten(cid:173)
`sity m the region longer than 600 nm, however, is insufficient to reproduce reddish colors
`correctly To improve this shortcoming, various combinations of phosphors have been
`investigated to realize a continuous emission spectrum close to that of reference light
`sources such as synthetic daylight and full radiator (blackbody radiator) Lamps con(cid:173)
`structed with this concept are called wide-band spectrum lamps For ordinary lamps, only
`the general color rendering index Ra is specified because these lamps are produced with
`
`1
`
`Note
`
`Fron
`
`calcium I
`rendering
`of the typ
`cation is i
`tant m da
`rendering;
`R9, is spe
`rendering
`mspectio
`are show
`
`Flue
`fluoresce
`the emiss
`wavelenj
`light sou
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`Phosphor Handbook
`
`ij
`
`Chapter five Phosphors for lamps
`
`369
`
`Table 4 Minimum Values of Color Rendering Indices of Fluorescent Lamps with
`Wide Emission Bands
`
`Classification
`of color
`rendering
`property
`
`Ordinary type
`
`Color rendering
`A
`Color rendering
`AA
`
`Color rendering
`AAA
`
`Light source
`color
`
`Daylight
`Day white
`White
`Warm white
`Incandescent color
`Day white
`Incandescent color
`Daylight
`Day white
`White
`Warm white
`Daylight
`Day white
`Incandescent color
`
`Symbol
`
`D
`N
`W
`WW
`L
`N-DL
`L-DL
`DSDL
`N-SDL
`W-SDL
`WW SDL
`DEDL
`N-EDL
`L-EDL
`
`From JIS Standard Z 9222 1990 With permission
`
`Minimum value of color rendering index
`Ra
`RIO
`R9
`Rll
`R12
`R13
`R14
`R15
`
`69
`67
`57
`54
`50
`75
`65
`88
`86
`84
`82
`95
`95
`90
`
`76
`72
`68
`64
`88
`88
`80
`
`65
`50
`88
`86
`84
`82
`93
`93
`88
`
`88
`88
`78
`
`93
`93
`85
`
`88
`90
`78
`
`93
`93
`85
`
`93
`93
`90
`
`0.45
`
`n JIS Standard Z 9112,
`
`it Lamps
`
`81
`
`(D)
`
`(CW)
`(W)
`(WW)
`
`lamps employ cal-
`tra Emission inten-
`duce reddish colors
`osphors have been
`t of reference light
`liator) Lamps con-
`rdinary lamps, only
`are produced with
`
`Table 5 Minimum Value of Color Rendering Indices of Three-Band Fluorescent Lamps
`Minimum value of
`color rendering index
`Ra
`R15
`
`Light source color
`
`Symbol
`
`Minimum value of
`three-band radiant flux ratio
`(r.)
`50
`50
`
`Day white
`Incandescent color
`
`EX-N
`EX-L
`
`80
`78
`
`80
`78
`
`Note
`
`P» +Pr.+P,
`-xlOO
`K
`where PB, PG PR are radiant flux within the wavelength ranges of 445-470 525-550 and
`595-620 nm, respectively PT is total radiant flux within the visible wavelength region
`From JIS Standard Z 9112 1990 With permission
`
`calcium halophosphate phosphors alone For lamps belongmg to the category of color
`rendering A, the special color rendermg index R15, which corresponds to the reproduction
`of the typical Japanese female face skin color, is specified in addition to Ra This specifi(cid:173)
`cation is understandable because color reproduction of facial appearances is very impor(cid:173)
`tant m daily human interactions Type AA lamps are required to have the necessary color
`rendermg properties for use m general lighting Another special color rendering index,
`R9, is specified for this purpose For color rendering AAA type lamps, all the special color
`rendermg indices are specified in order to meet such applications as color evaluation and
`inspection Typical spectral power distribution curves of the wide-band emission lamps
`are shown in Figure 3
`
`Fluorescent lamps with narrow emission bands The distinctive features of this type of
`fluorescent lamp is that it possesses a discontmuous spectral power distribution Most of
`the emission is intentionally concentrated in specific wavelength regions In the rest of the
`wavelength region, no or very weak emission is produced As is well known, most natural
`light sources produce a contmuous spectrum Efforts to improve the color rendering of
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`

`400
`
`500
`600
`700
`Wavelength (nm)
`
`Figure 4 Spectral
`Haft,HH and The
`
`Figure 3 Spectral power distribution curves of fluorescent lamps with wide emission bands.
`
`artificial light sources concentrated on how to realize spectral power distributions approx(cid:173)
`imating those of the natural light throughout the entire visible wavelength range. High
`color rendering lamps with the wide-band emission are based on this concept. In imple(cid:173)
`menting this concept, part of the emission energy was generally distributed to the both
`ends of the visible wavelength region, i.e., deep blue and red, resulting in the decrease of
`the total luminous efficacy of the lamps. This means that high luminous efficacy and high
`color rendering properties cannot stand together.
`This limitation, however, has been eased by developing a better understanding of the
`chromatic response of the human eye. Since 1970, extensive research on the color vision
`of the human eye has been carried out. As a result, it became clear that the color discrim(cid:173)
`ination sensitivity of the human eye depends strongly on the wavelength, as does the
`sensitivity for brightness. It was confirmed that the sensitivity of the human eye is con(cid:173)
`centrated within a relatively narrow spectral region centered at 450, 540, and 610 nm. It
`was also confirmed that most colors can be reproduced using a light source with an
`emission spectrum consisting a combination of very narrow emission bands at these
`wavelengths. Calculated results suggest the possibility of attaining Ra 85 lamps by a simple
`combination of these three emission lines.23 These research results offered alternate means
`to improve the color rendering property of fluorescent lamps. According to this new
`concept, high efficacy and high color rendering are compatible with each other because it
`is no longer necessary to distribute emission energy into regions of low luminous sensi(cid:173)
`tivity. The first report of a fluorescent lamp based on this new concept was made by Haft
`and Thornton in 1972.4 They obtained an Ra 83 lamp having a color temperature of 4200K
`using the phosphor combination of 3Sr3(P04)2 SrCl2:Eu2+, Zn2Si04:Mn2+, and Y203:Eu3+ as
`the blue-, green-, and red-emitting components, respectively. The luminous output was
`comparable to that of ordinary lamps with calcium halophosphate phosphors. The spectral
`power distribution curve of this lamp is shown in Figure 4. This lamp illustrated the new
`concept, but was not commercialized due to the relatively poor maintenance characteristics
`of the phosphors.
`The commercialization of a practical lamp had to wait for the development of better
`phosphors for this purpose. In 1974, a series of rare-earth activated aluminate phosphors
`was invented by Verstegen.5 Fluorescent lamps employing BaMg2Al16027:Eu2+ as the blue-
`emitting component, CeMgAlnO^Tb3-"- as the green-emitting component, and Y203:Eu3+ as
`the red-emitting component offered equivalent luminous output to that of the lamps
`employing the common calcium halophosphate phosphor; the lamps attained an Ra value
`as high as 85 throughout the color temperature range of 2500 to 6500K.6 An example of the
`
`Figure 5 Spectr.
`Verstegen, J.M.P.
`permission.)
`
`spectral power
`is obvious that
`region than do
`Since that t
`commercially c
`throughout. Ti
`announcement
`Overall, howe1
`Figure 6 depic
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`

`Phosphor Handbook
`
`Chapter five: Phosphors for lamps
`
`371
`
`1UU
`
`1
`
`Si"
`j-
`b 80
`w (U
`-
`&
`60
`O
`ft <u 40
`>
`5 20
`«
`0
`300 350 400 450 500 550 600 650 700 750
`Wavelength (nm)
`
`rJ\
`
`r\
`. lAtj\j yi\^A
`
`;mission bands.
`
`stnbutions approx-
`ength range. High
`concept. In imple-
`•ibuted to the both
`; in the decrease of
`s efficacy and high
`
`iderstanding of the
`on the color vision
`t the color discrim-
`ength, as does the
`human eye is con-
`540, and 610 nm. It
`;ht source with an
`on bands at these
`5 lamps by a simple
`•ed alternate means
`)rding to this new
`ich other because it
`)w luminous sensi-
`was made by Haft
`nperature of 4200K
`'+, and Y203:Eu3+ as
`ninous output was
`!phors. The spectral
`illustrated the new
`ance characteristics
`
`/elopment of better
`uminate phosphors
`D27:Eu2+ as the blue-
`nt, and Y203:Eu3+ as
`that of the lamps
`ttained an Ra value
`6 An example of the
`
`n
`
`I I-,
`
`Figure 4 Spectral power distribution of a fluorescent lamp with narrow emission bands. (From
`Haft, H H. and Thornton, W A, /. Ilium. Eng. Soc, 2-1, 29,1971. With permission.)
`
`80
`
`60
`
`40
`
`S c
`
`a.
`
`o
`Q.
`u
`>
`
`Pi
`
`20-'M J ^-A
`
`400
`
`600
`500
`Wavelength (nm)
`
`700
`
`Figure 5 Spectral power distribution of a fluorescent lamp with narrow emission bands (From
`Verstegen, J.M.P.J., Radielovic, D., and Vrenken, L E, /. Eledrochem. Soc, 121, 1627, 1974 With
`permission.)
`
`spectral power distribution is shown in Figure 5. From a comparison of Figures 4 and 5, it
`is obvious that the latter has a much sharper and more intense emission band in the green
`region than does the former. This contributes to the higher luminous output.
`Since that time, various blue- and green-emitting phosphors have been developed and
`commercially deployed; the red-emitting component, Y203:Eu3+ has remained the same
`throughout. The lamp efficacy has also been improved from 80 1m W"1 at the time of first
`announcement to nearly 100 1m W"1 when combined with energy-saving lamp designs.
`Overall, however, the spectral power distribution curve has remained almost the same.
`Figure 6 depicts a typical example of the spectral power distribution of a 5000-K lamp of
`
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`

`Phosphor Handbook
`
`Chapter five:
`
`being used
`manufactui
`Section 5.3.
`
`Referenc
`1. JIS s
`2. Thor
`3. Koec
`4. Haft
`5. Versl
`6. Vers
`7. Taka
`
`400
`
`600
`500
`Wavelength (nm)
`
`700
`
`Figure 6 Spectral power distribution of a 5000K three-band fluorescent lamp.
`
`the three narrow emission band type (usually called three-band lamp), which is most commonly
`used in Japan today.
`The addition of an extra emission in the 490-nm region increases the Ra value to 88
`with only a small sacrifice of lamp efficacy.7 For this purpose, several kinds of blue/green-
`emitting phosphors are being used in commercial lamp products in Japan. The highest Ra
`values can be obtained by adding a deep red emission. However, this decreases the lamp
`efficacy.
`Illumination by the narrow-band lamps produces several specific lighting effects that
`are not observed when conventional lamps are used. First, under illumination by a narrow(cid:173)
`band lamp, the required illuminance level can be lowered from that produced by ordinary
`lamps to give a sensation of an equivalent brightness in places where chromatic color
`objects exist. That is, the human eye senses a higher brightness under illumination by the
`narrow-band lamps than by ordinary lamps when the illuminance level is equivalent.
`Although this effect has commonly been observed experimentally under illumina(cid:173)
`tion—even using conventional, high color rendering lamps of wide emission band—the
`effect was not recognized in the practical situation due to the extremely low luminous
`output of these lamps. In the case of narrow-band lamps, this effect is observed because
`these lamps have equivalent luminous output to that of the ordinary lamp. Second, the
`light from the narrow-band lamps reproduces the object color preferably and vividly.
`Finally, illumination by the narrow-band lamps gives a clear and limpid appearance to
`color objects. All these effects are considered to originate from the distinctive emission
`spectrum of the narrow-band lamps. As for the detail of color rendering indices, refer to 17.6.
`
`Phosphors utilized for three-band lamps. Phosphors presently utilized for three-band
`lamps are shown in Table 6. (Sr,Ca,Ba)5(P04)3Cl:Eu2+ and BaMg2Al16027:Eu2+ are two main
`classes of blue-emitting phosphors. The ratio of Ca:Ba:Sr of the former phosphor differs
`from manufacturer to manufacturer in order to optimize the emission spectrum according
`to a specific lamp design. For the latter phosphor, partial replacement of Ba by other alkaline
`earth metals and small deviation from the formulated composition are also introduced by
`various manufacturers to optimize the emission spectrum. As for the green-emitting phos(cid:173)
`phors, three kinds of phosphors—namely CeMgAl11019:(Ce3+):Tb3+, LaP04:Ce3+:Tb3+ and
`GdMgB5O10:Ce3+:Tb3+—are being used. YjOjiEu3* remains the only available phosphor for
`the red-emitting component. For the purpose of improving Ra values, blue/green-emitting
`(Ba,Ca,Mg)5(P04)3Cl:Eu2+, Sr4All4025:Eu2+ and 2SrO-0.84P2O5 0.16B2O3:Eu2+ phosphors are
`
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`

`Phosphor Handbook
`
`Chapter five: Phosphors for lamps
`
`373
`
`Table 6 Phosphors Utilized in Three-Band Lamps
`Emission color
`Chemical composition
`(Sr,Ca,Ba)5(P04)3Cl:Eu2+
`Blue
`BaMg2Al16027-Eu2+
`C e M g A ^ A ^ C e ^ iW
`LaP04:Ce3t:Tb3t
`GdMgB5O]0:Ce3*:Tb3+
`Y203:Eu3+
`
`Mam
`
`Green
`
`Red
`
`Auxiliary
`
`Blue-green
`
`(Ba,Ca,Mg)5(P04)3Cl:Eu2*
`2SrO 0.84P2O5 0.16B2O3:Eu2+
`Sr4Al14025 Eu2+
`
`being used. The actual combination of these phosphors used in lamps varies either by
`manufacturer or lamp type. Detailed characteristics of the phosphors are described in
`Section 5.3.2.
`
`References
`1. JIS Standard Z 9112,1990.
`2. Thornton, W.A., / Opt. Soc. Am., 61, 1155, 1971.
`3. Koedam, M. and Opstelten, J.J., Lighting Res. Tech., 3, 205,1971.
`4. Haft, H H. and Thornton, W.A., / Ilium. Eng Soc, 2-1, 29,1972
`5. Verstegen, J.M.P.J., /. Eledrochem Soc, 121, 1623,1974.
`6. Verstegen, J.M.P.J., Radielovic, D., and Vrenken, L.E, /. Electrochem Soc, 121,1627, 1974.
`7. Takahashi, M., Shibata, H., and Iwama, K, Natl. Tech. Kept, 38, 582,1992.
`
`is most commonly
`
`the Ra value to 88
`nds of blue/green-
`an. The highest Ra
`iecreases the lamp
`
`ighting effects that
`lation by a narrow-
`duced by ordinary
`re chromatic color
`Uumination by the
`evel is equivalent.
`' under illumina-
`nission band—the
`tely low luminous
`observed because
`lamp. Second, the
`rably and vividly,
`pid appearance to
`istinctive emission
`idices, refer to 17.6.
`
`zed for three-band
`Eu2+ are two main
`r phosphor differs
`pectrum according
`5a by other alkaline
`also introduced by
`een-emitting phos-
`iP04:Ce3+:Tb3+ and
`lable phosphor for
`ue/gre en-emitting
`,u2+ phosphors are
`
`i':
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`NICHIA EX2019
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`

`\ x A
`
`\
`
`\
`
`\l \
`
`s-s-
`
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`\
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`\
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`k
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`X \
`\\ \1
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`v\
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`0.36
`
`0 34
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`n 39
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`^
`
`0.18
`
`0.20
`
`0.22
`
`0.24
`
`0.26
`
`0 28
`
`Figure 8 Locus of the color of the Planckian radiator m CIE 1964 chromaticity diagram for a wide
`range of color temperatures (From CIE, Testing of Supplementary Systems of Photometry, TC1-21, m
`preparation With permission)
`
`27.6 Color rendering
`17.6.1 Methods of measurement
`
`Color rendering is the property of the light source that changes the colors of the object
`illuminated by that light source. To deal with the color rendering, the following two
`methods are normally employed.
`The first method is psychophysical. The basic approach of this method is to examme
`how the color of an object illuminated by a sample light source compares with the color
`observed under illumination with a reference light source having an ideal color rendering.
`The second method, on the other hand, is psychological. The approach of this method
`is to examme by visual observation whether the color of an object under a sample light
`source is preferred by the observer or not. To conduct these observations, a careful selection
`of the colors to be examined is essential. Since this method is subjective, no definite method
`to determine this kind of color rendering has been developed. However, in some cases,
`the results derived by this method are practically more relevant and important than the
`results obtained through the psychophysical method.
`To examine the color rendering properties of a sample light source based on the
`psychophysical method, colors of a number of objects illuminated by a sample light source
`are compared psychophysically with the colors obtained when the objects are illuminated
`by a reference light source. For this purpose, the chromaticity points of object colors are
`calculated with the CIE colorimetric system already described. Before the chromaticity
`points can be calculated for the reference light source, the spectral energy distributions
`and the color temperature of the reference light must be specified.
`
`Chapter seventeen
`
`The CIE spe
`lations. The first
`To examine the
`reference light s
`correlated color
`lower than 50001
`for temperature
`recommended.
`The two cui
`Planckian radiat
`temperature is ta
`of the Planckian
`
`27.6.2 Color
`
`i
`17.6.2.1
`The color rendei
`light source. Th
`sample light sou
`the chromaticity
`each of eight sel
`ences. If no col<
`rendering index
`difference is, the
`as to the limits c
`the indices is ah
`
`27.6.2.2
`Special color rei
`CIE. The special
`shows the close
`color temperatu
`The special
`way to the gem
`is calculated inc
`selected to repr<
`with a high chro
`are expressed ac
`standard, the cc
`
`27.6.3 Gene?
`To use the genei
`limitation of its
`
`1. No valid
`Ra betwe
`for light
`two light
`no actual
`es vary f
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`osphor Handbook
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`Chapter seventeen: Color vision
`
`815
`
`The CIE specifies two series of Reference Light Sources to be used for these calcu(cid:173)
`lations. The first is a Planckian radiator and the second is the CIE "daylight" standard.
`To examine the color rendering of a sample light source, it is recommended that a
`reference light source with a color temperature lying within a range of 5 mireds of the
`correlated color temperature of the sample light source be used. For color temperatures
`lower than 5000K, it is recommended that the Planckian radiator be used. As a standard
`for temperatures higher than 5000K, on the other hand, the CIE daylight standard is
`recommended.
`The two curved lines in Figure 8 show the loci of the chromaticity points of the
`Planckian radiator and the CIE daylight reference light sources, respectively. The color
`temperature is taken as a parameter. The dotted curve shows the overlap zone of the locus
`of the Planckian radiator with that of the CIE "daylight" standard.
`
`27.6.2 Color rendering index
`17.6.2.1 General color rendering index (RJ
`The color rendering index (RJ indicates the extent of the color rendering properties of a
`light source. The basis of the calculation of the general color rendering index (RJ of a
`sample light source is the use of color differences. This difference is the distance between
`the chromaticity points of the sample and the reference light source, and is obtained for
`each of eight selected object colors. Ra is calculated by taking the average of these differ(cid:173)
`ences. If no color difference is found for all eight object colors, then the general color
`rendering index (RJ is the maximum, 100; it is observed that the larger the averaged
`difference is, the lower the Ra figure. To use these estimates, however, care must be taken
`as to the limits of applicability and the meanings of the indices. Careful interpretation of
`the indices is always necessary. Some of the pitfalls encountered are discussed below.
`
`17.6.2.2 Special color rendering indices
`Special color rendering indices are calculated for one of six test colors specified by the
`CIE. The special color rendering index of a sample light source for one of the test colors
`shows the closeness of that test color to that under a reference source having the same
`color temperature.
`The special color rendering indices of a sample light source are calculated in a similar
`way to the general color rendering indexes. However, the special color rendering index
`is calculated individually for each of the following six selected colors. The six colors are
`selected to represent the colors of normal objects. They are red, yellow, green, blue, each
`with a high chroma, and the colors of a Caucasian complexion and a green leaf. The indices
`are expressed according to the selected colors as R,, R10, Rn, Ri2, R^, and R14. In the Japanese
`standard, the color of an Oriental complexion is added as R15.
`
`17.6.3 General color rendering index and perceived colors
`To use the general color rendering index Ra, some caution is necessary, since there is some
`limitation of its applicability. Some of these limitations are summarized below.
`
`1. No valid comparisons can be made using only the general color rendering index
`Ra between lights with different color temperatures. A difference in Ra is valid only
`for light sources with similar color temperatures. If the color temperatures of the
`two light sources to be compared are considerably different, then the difference has
`no actual meaning. This is because the perceived colors under reference light sourc(cid:173)
`es vary for different color temperatures.
`
`0.28
`
`iagram for a wide
`ometry, TC1-21, in
`
`ors of the object
`e following two
`
`od is to examine
`2S with the color
`color rendering,
`•h of this method
`;r a sample light
`i careful selection
`> definite method
`•r, in some cases,
`iportant than the
`
`ce based on the
`tnple light source
`s are illuminated
`object colors are
`the chromaticity
`rgy distributions
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`Phosphor Handbook
`
`Chapter seventeen
`
`2. Judgment of the perceived colors cannot always be made between light sources
`with low Ra values. As described, the Ra value is calculated using an average of the
`color differences for the eight specified test colors. As can be easily seen, this average
`can be obtained with many different combinations of the color differences.
`This implies that the color rendering properties can be considerably different,
`even if the 1^ value is the same. For example, one lamp may have color rendering
`properties that cause a color difference for all eight test colors nearly to the same
`extent. Another lamp, on the other hand, may have other color rendering properties
`that cause considerable color differences for some of the test colors, whereas there
`is almost no color difference for the remaining test colors. If the latter lamp is used
`in an application where only some colors are to be perceived correctly and the lamp
`causes no big color difference in these colors, then the color rendering properties
`of the lamp are effectively comparable to another lamp with a very good Ra value.
`3. Another aspect of importance is that a very high Rj, value for a lamp only means
`that the colors perceived under its illumination are similar to the colors under the
`reference light source. Sometimes, however, colors that are slightly different from
`the reference colors are preferred. As the above examples show, the color rendering
`properties of such lamps cannot be judged correctly solely by the Ra value.
`
`27.6.4 Color appearance of light sources and perceived colors
`
`As described, the influence of the difference in the color temperature of the light sources
`on the perceived color is compensated, at least partly, by chromatic adaptation. Lamps of
`the same color temperature, however, can be made with many different spectral energy
`distributions. For this reason, the color rendering properties of lamps with the same color
`temperature can differ considerably because their spectral energy distribution is different.
`
`27.6.5 Color rendering and brightness
`
`The stimulus that yields the brightness sensation is the luminance. However, if one
`observes an object carefully, the perceived brightness of the object can be different, depend(cid:173)
`ing on its colors, even if they have the same luminance. Experimental observations revealed
`that the sensation of illuminated objects being lighter or darker in a room depends very
`much on the color rendering properties of the light source employed.13 These comparisons
`were made in a room illuminated with fluorescent lamps of different Ra values and with
`an incandescent lamp with an Ra value of 100. The results are shown in Figure 9, in which
`the ratio of the illuminance under the incandescent lamp to that under the test fluorescent
`lamps to obtain the equivalent subjective brightness is plotted as a function of the R^ value
`of the test lamps. It is observed that, with decreasing Ra of the test lamps, the illuminance
`under those lamps necessary to obtain the equivalent subjective brightness increases
`remarkably.
`
`27.7 Other chromatic phenomena
`27.7.2 Purkinje phenomenon
`This phenomenon was named after the Czech psychologist Purkinje, who discovered it
`in the early 19th century. The phenomenon concerns variation in the relative lightness of
`perceived colors between red and blue with changes in the luminance of the field of view.
`As the field becomes darker, the perceived red colors become relatively darker than the
`blue colors.
`
`Figure 9 Relatior
`(Ev(Ld)/Ev(i)) and
`lamp with Ra of V
`imoto, K., and Kic
`
`27.7.2 Metan
`
`Metamerism is a
`reflection factors
`requires a prope
`energy distributi
`
`27.7.3 Bezoh
`
`The Bezold-Bmc
`constant spectra
`is varied. A defii
`yet been estabhs
`
`27.7.4 Helml
`The Helmholz-I
`be lighter than a
`
`References
`1 Cm, The B
`1. Leonardo
`3. Newton, S
`4. Young, Th
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