`
`January 1977§9g
`
`Volume 6/Number 2
`
`Jflll
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`_ of the Illuminating Engineering Society
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`nghtlng In the logging and sawmill industries
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`67
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`Technical Committee Report
`
`Ultraviolet radiation—considerations ln interior lighting design
`R. E. Levin, G. Ft. Spears, G. W. Clark and E. D. Biokford
`
`Improved color rendition in high pressure mercury vapor lamps
`Mary V. Hoffman
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`The design of safety-colors
`W. A. Thornton
`
`Tungsten-halogen lamp dosed with tin tetralodlde
`A. D. Kulkarni. J. Martin and H. G. Sell
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`An automated high-speed photometer
`I'_. C. Snyder and P. E. Westlake
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`80
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`89
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`92
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`100
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`105
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`Recommended practice for the specification of an ESI rating in
`interior spaces when specitic task locations are unknown
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`111
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`Technical Committee Report
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`Discussion of previously publlshed papers
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`124
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`I.
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`ished quarterly in the United States of America by the Illuminating Engineering Society of North America. 345
`:4'nh St.. New York. N.Y. 10017. Copyright. Illuminating Engineering Society of North America. 197?. Sec-
`class postage paid at New York. N.Y. and additional mailing ottlces. This publication is indexed regularly
`Engineering Index. inc... and is available on microfilm from University Microfilm, Ann Arbor. Mich. 43106.
`scription rates: $25.00 for few annual issues. plus extra postage to all countries In which second-class postage
`3 do not apply. Single copies: $2.50 to members: $6.25 to nonmembers. Editorial Office. 345 East 47th St..
`' York. N.Y. 1001?. Printing Office. Easton. Pa.
`
`-
`Clifford L' Forbes J" EdItor
`Jack F- Christensen Associate Editor
`John E. Kaut'man Technical Director
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`Howard Haynes Engineering Assistant
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`C. L. Crouch Director of Research lERl
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`TCL 1021, Page 1
`TCL 1021;
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`Improved color rendition
`in high pressure me’icury vapor lamps
`
`Mary V. Hoffman
`
`The addition of Y3Ai5012:0e to the group of phosphors suitable for color
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`correcting the mercury discharge lamp provides for Improving the color
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`rendering Index without a lumen loss. By altering the cerium content in the
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`tormulatlon, the absorption and brightness can be adjusted to its optimum
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`value in the lamp.
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`TCL 1021, Page 2
`TCL 1021 i‘
`89
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`this substitution. Combinations of these two phos-
`phors can be used, as described by Rokosz, et GL4
`We have found another phosphor, cerium-acti-
`vated yttrium aluminate garnet (YAG:Ce) which is
`useful in improving color rendition by absorbing the
`blue Hg radiation and also adds to the total emission
`of the lamp by converting this blue radiation into
`emission centered at 560 nanometers. It can be
`combined with the Y(VP)O4:Eu emission, effectively
`changing the Color of the lamp.
`Lamps prepared with blends of YAG:Ce and YVP
`phosphors Show the shift in color points from below
`the black body to, on, or above the locus, depending
`on the proportions used. Typical color points are
`shown in Fig. 1 for a warm color corrected lamp. The
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`Figure 1. Color shifts with increasing YAG:Ce In YlVP)
`04:Eu.
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`YAOO
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`.4l0
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`.390
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`.400
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`.410
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`.420
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`.430
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`I
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`The ideal in color rendition of a high pressure mer-
`cury discharge lamp has been the subject of several
`recent papers, in which simulated spectral distribu-
`tions have been created by the addition or subtrac-
`tion of spectral energy.1-2 This can be done to obtain
`lamps of selected color temperatures, with various
`combinations of real and simulated phosphor emis—
`sions. The optimization of the luminous efficiency
`can be calculated in the same manner. One study has
`shown that the addition of emission at 620 nanome-
`
`ters to the Hg discharge is near the optimum for color
`rendition, but that for lamps with color temperature
`of 4000 to 3000 kelvins, it is necessary to remove some
`of the Hg discharge in the blue. For luminosity, ad—
`ditizoan of emission near 590 nanometers is need-
`ed. -
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`Among the existing phosphors meeting the tem-
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`perature and stability requirements of the mercury
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`discharge lamps, only Y V04zEu and Y(VP)04:Eu
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`phosphors (YVP) supply emission at the necessary
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`spectral region, with the main peak at 618 nanome-
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`ters. They do not provide absorption of the blue Hg
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`lines in sufficient amount or emission in the high
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`luminous region. Filtering of the blue can be obtained
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`by the addition of a pigment or of a phosphor which
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`also acts as a pigment. The phosphor magnesium
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`fluogermanate activated with manganese (MG) is the
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`only suitable red emitter with appreciable absorption
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`of the blue lines, but since the emission is at 650 to
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`660 nanometers, the luminosity is not enhanced by
`
`A paper presented at the Annual IES Conference. August ‘29
`
`through September 2, 1976, Cleveland, Ohio. AUTHOR: General
`
`Electric Company, Cleveland, Ohio.
`
`
`

`

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`color shift is due largely to the absorption of the 436
`nanometer Hg line, which is filtered by about 40
`percent with 15 percent YAG in the blend. The lu-
`minosity of the lamps remains about the same for
`four lamp colors shown. This is due to the efficient
`conversion of the 436 Hg line into visible emission.
`These data are summarized in Table I.
`
`The actual color points obtained can be varied by
`the amount of phosphor used on the lamp as well as
`the proportion of YAG:Ce in the blend. It can also be
`
`varied by using the blend over a pre-coat, as de-
`scribed by Rokosz, et all.4 The pro-coat acts as a re-
`flector for both ultraviolet and the blue radiation,
`allowing better utilization of the Hg radiation by the
`phosphors. With the YAG:Ce present, the reflection
`of the blue radiation increases its effect both as a
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`pigment and as a phosphor.
`The YAGzCe phosphor, which was developed for
`its emission characteristics under cathode ray exci-
`tation516 is strongly absorbing in the blue, as shown
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`to
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`0.9
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`0.8
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`0.?
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`0.6
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`0.5
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`0.4
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`0.3
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`
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`DIFFUSEREFLECTANCE
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`
`
`RELATIVE1NTENS'ITY
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`300
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`400
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`500
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`600
`
`T00
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`WAVELENGTH, n m
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`L...—._J_.L_L__
`330 340 350 360
`nm
`
`
`420
`430 440 450 460
`470 480
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`WAVELENGTHm m
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`Figure 2. Diffuse Reflectance curve, "2.925 Gem-,5);
`Also”.
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`Figure 3. Excltation curve: detected wavelength—511
`nanometers.
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`Figure 4. Emission curve: excitation wavelength—436
`nanometers.
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`Figure 5. Emission intensity vs cerium content. measured
`at 25° c and 300° c. Excitatlon wavelength—436 nm.
`_._—-.-—
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`at 25°C
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`RELATIVE1NTENSITY
`
`
`/
`/-—u1 25° c
`
`no
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`lNTENSITY 8
`
`I00
`
`TO
`
`0.005 0.010
`
`0.030
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`0.020
`1
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`JOURNAL OF IESIJANUARY 197?
`TCL 1021, Page 3
`TCL 1021, Page 3
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`
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`sec
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`720
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`I
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`430
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`500 640
`520 560
`WAVELENGTH, n m
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`90
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`

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`Table l—Lamp data:YAG:Ce with YlVPlo, :Eu
`Percent
`loo—hour
`
` YAG:Ce lmlw X Y
`
`
`
`
`
`0
`5
`10
`15
`
`51.5
`52.1
`50.7
`51.3
`
`.408
`.411
`.420
`.426
`
`.384
`.394
`.403
`.411
`
`CRI
`
`45
`—
`—
`51
`
`4. F'. Rokosz, J. W. Sauaville, and J. Van Broekhoven, “Incu-
`descent lamp color with high-intensity discharge lamps," JOUR-
`NAL or THE ILLUMINATING ENGINEERING SOCIETY, Vol. 3, No.
`1, October 1973, p. 95.
`5. G. Blasse and A. Bril, “A new phosphor for flying-spot cath-
`ode-ray tubes for color television: yellow-emitting Y3A15012:Ce,"
`Applied Physics Letters, Vol. II, No. 2, July 15, 1967, p. 53.
`6. W. W. Holloway, Jr. and M. Kestigian, “Optical propertim of
`cerium-activated garnet crystals,“ Journal of the Optical Society
`of America, Vol. 59, No. 1, January 1969, p. 60.
`
`by the diffuse reflectance curve (see Fig. 2), and is
`also excited by this radiation. This absorption is into
`the 5d state of the cerium, which in this crystal
`structure, lies in an unusual position. Cerium usually
`absorbs in the ultraviolet and emits inthe near ul-
`
`traviolet or in the blue. The YAG:Ce phosphor is not
`excited by 254 nanometers and only weakly by 365
`nanometers from the Hg arc. The excitation spectra
`(See Fig. 3) shows the very strong dependence of-the
`emission intensity on the 436-nm Hg radiation.
`The emission of the phosphor is in a band peaking
`at about 540 nanometers at 25 ° C shifting to about
`560 nanometers at 300° C (See Fig. 4). This is at the
`maximum eye sensitivity and close to the calculated
`peak of 590 nm for good lumen output in the sys-
`tem.
`
`As with most phosphors, the specific conditions of
`the lamp determine its applicability, and the com-
`position can often be altered according to its use. In
`the YAG:Ce phosphor, the cerium concentration is
`the critical factor. Both the absorption at .436 na-
`nometers and the emission intensity increase with
`the cerium concentration with the brightness
`reaching a maximum at about one- to two-atom
`percent and the absorption at about three-atom
`percent when measured at 25° C. At the temperature
`of operation of the lamp, the phosphor is less effi-
`cient, and brightness measurements made at 300° C
`show that lower cerium concentrations are desirable.
`
`As shown in Fig. 5, a rather narrow range of cerium
`content must be maintained for the best conversion
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`of 436 radiation to emission at 560 nm in the lamp.
`
`References
`
`l. J. J. Opstelten, D. Radielovié and W. L. Wanmaker, “The
`choice and evaluation of phosphors for application to lamps with
`improved color rendition,“ Journal of the Electrochemical So-
`ciety, Vol. 120. No. 10. October 1973, p. 1400.
`2. T. F. Soules and M. A. Meier, “Optimized spectral power dis-
`tributions for mercury vapor lamps," Journal of the Electro-
`chemical Society, Vol. 121, No. 3, March 1974, p. 407.
`3. H. Ivey, “Color and efficiency of fluorescent and fluoro-
`rescent-mercury lamps," Journal of the Optical Society of
`America, Vol. 62, 1972, p. 814.
`
`DISCUSSION
`
`W. A. THORNTON" The high pressure mercury vapor lamp is
`in need of all the kindly attention it can get. This welcome paper
`brings better lamp performance closer. It performs a service by
`bringing another useful phosphor into the very limited line-up of
`luminescent materials that can endure the operating conditions
`in this lamp. The new phosphor has the useful property of com
`verting undesired blue-violet arc emission to desired green light,
`which tends to improve both color rendering and output. Does the
`increase in Color Rendering Index (CRI), as 15 percent of the new
`phosphor is added, represent a real visual improvement in color
`rendering of real objects and scenes? As to the proposed addition
`of yellow wavelengths near 590 nanoeters “for good lumen output.
`in the lamp system,” we believe that such addition would harm
`color rendering more than it would improve lumen output. The
`usefulness of the new YAG:Ce phosphor is, we believe, due to the
`fact {see Fig. 4) that it contributes green light and red light; that
`it also contributes yellow light is a disadvantage. The Scales and
`Meier study (see Reference 2) makes clear that peak lumen output
`by use of yellow light is accompanied by color rendering index of
`—20. Reference 1 ascribes poor color rendering to yellow emitting
`phosphors. Has the author any prospect of an efficient phosphor
`emitting a narrow band near 490 nanometers, which, according
`to the same references, can help raise CRI further?
`
`Aura-Ion:l The true test of improved color rendition always rests
`on a subjective visual evaluation, especially in a system such as this
`one, with about ten percent calculated change in CRI. No sys-
`tematic evaluation of this lamp system has been made, but the
`general appearances have been favorable.
`The emission contribution of YAG:Ce (if present as the only
`phosphor) would definitely result in a lower CRI. The Soules and
`Maier paper points to a system that closely approximates a pure
`YAG:Ce lamp. It has a CRI of 23. The usefulness of the YAG:Ce
`lies in its ability to absorb the 436-nm Hg line to the extent suffi-
`cient to improve the CRI, and supply enough emission to con-
`tribute to the lumen level. at a relatively low weight percent.
`The Scales and Meier paper ascribes the CR1 of ---20 to a system
`containing a narrow band emission at 580 nanometers. when
`combined with bluer line emission, but shows that when Eu.+3
`emission is present the CR] cannot fall that low.
`"‘ Westinghouse Electric Corporation, Bloomfield, New Jersey.
`1‘ The author wishes to acknowledge the help of Dr. T. F. Soules
`for numerous discussions and E. Homonnay for the testing in
`lamps.
`
`Information for authors
`
`to the review at the Papers Committee of the IE6.
`
`The JOURNAL OF THE IE5 is publlahed quarterly by the Iilurnlnailng Engl-
`neerlng Soclety of North America. Manuscripts should be senl to the editor,
`345 East 47th Street, New York, N. Y. 10017. All manuscrlpts are subject
`
`JOURNAL OF “is I JANUARY 1977
`
`
`
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`TCL 1021, Page 4
`TCL 1021
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`TCL 1021, Page 5
`TCL 1021, Page 5
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`ILLUMINATING 2
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`SOCIETY
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`JOURNAL
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`5-7
`
`OCT. 1975-
`JULY 1978
`
`TCL 1021, Page 6
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