`
`t
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`January 1977§92
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`Volume 6/Number 2
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`JlililiiiiilQ
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`‘ of the Illuminating Engineering Society
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`Lighting In the logging and sawmill Industries
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`67
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`Technical Committee Report
`
`Ultraviolet radiation—considerations in interior lighting design
`R. E. Levin, G. Fl. Spears. G. W. Clark and E. D. Bickford
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`Improved color rendition in high pressure mercury vapor lamps
`Mary V. Hoffman
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`The design oi safety-colors
`W. A. Thornton
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`Tungsten-halogen lamp dosed with tin tetralodide
`A. D. Kulkarni, J. Martin and H. G. Sell
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`An automated high-speed photometer
`L. 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 lor the specification ol an ESI rating in
`interior spaces when specific task locations are unknown
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`111
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`Technical Committee Report
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`Discussion oi previously published papers
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`124
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`lshed quarterly in the United States of America by the Illuminating Engineering Society of North America, 345
`:47ih St.. New York. N.Y. 10017. Copyright, Illuminating Engineering Society of North America. 197?. Sec-
`class postage paid at New York. NY. and additional mailing offices. This publication is indexed regularly
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`a 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.
`
`Cilflord L. Forbes Jr. Ediiar
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`53°“ F- Christensen Associate Editor
`John E. Kaufman Technical Director
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`O. L. Crouch Director of Research lERi
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`
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`LOWES 1021, Page 1
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`Howard Haynes Engineering Assistant
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`
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`
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`improved color rendition
`in high pressure mercury vapor lamps
`
`Mary V. Hoffman
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`The addition of Y3Ai5012:Ce to the group of phosphors suitable tor 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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`formulation, the absorption and brightness can be adiusted to Its optimum
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`value in the lamp.
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`this substitution. Combinations of these two phos-
`phors can be used, as described by Rokosz, et 01.4
`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 shitts with increasing YAG:C6 In Y(VP)
`O‘IEU.
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`YAHOO
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`.4IO
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`.390
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`.400
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`MO
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`.420
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`.430
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`LOWES 1021, Page 2
`LOWES 1021,
`89
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`The idea] 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}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-
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`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-
`ditizosn 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)O4: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
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`A paper presented at the Annual IES Conference, August 29
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`through September 2, 1976, Cleveland, Ohio. AUTHOR: General
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`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
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`varied by using the blend over a precast, as de-
`scribed by Rokosz, ct al.‘ 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 YAG:Ce phosphor, which was developed for
`its emission characteristics under cathode ray exci-
`tation5’6 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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`0.7
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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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`DIFFUSEREFLECTANCE
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`RELATIVEiNTENS'ITY
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`300
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`400
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`500
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`600
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`Too
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`WAVELENGTH, n m
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`1.....—._J._.l-_L__
`330 340 350 360
`nm
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`420
`430 440 450 460
`470 480
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`WAVELENGTHm m
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`Figure 2. Dilfuse Reflectance curve, 012.925 Cit-”75):,
`Al5012.
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`Figure 3. Excitation 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 are cerium content. measured
`at 25° c and 300° c. Excitailon wavelength—436 nm.
`_._—-.-—
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`90
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`at 25° C
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`RELATIVEINTENSITY
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`430
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`600 640 sec
`520 560
`WAVELENGTH, n m
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`720
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`I
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`/
`/-—o1 25° c
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`”0
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`INTENSITY 8
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`|00
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`70
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`0.005 0.0l0
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`0.030
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`0.020
`X
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`JOURNAL OF IESIJANUARY 1977
`LOWES 1021, Page 3
`LOWES 1021, Page 3
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`Table l—Lamp data:YAG:Ce with YlVPlO, :Eu
`Percent
`TOO—hour
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` YAG:Ce lm/w X ‘1'
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`0
`5
`10
`15
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`51.5
`52.1
`50.7
`51.3
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`.408
`.411
`.420
`.426
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`.384
`.394
`.403
`.411
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`MRI
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`45
`—
`—
`51
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`4. F. Rokosz, J. W. Sausville, and J. Van Broekhoven, “Incam
`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. Blasae and A. Bril, "A new phosphor for flying-spot cath-
`ode-ray tubes for color television: yellow-emitting Y3A1501220e,"
`Applied Physics Letters, Vol. II, No. 2, July 15, 1967, p. 53.
`6. W. W. Holloway, Jr. and M. Kestigian, “Optical properties of
`cerium-activated garnet crystals,” Journal of the Optical Society
`ofAmerica, 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 irr‘the 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.
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`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.
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`References
`
`l. J. J. Opstelten, I). Radiclovié 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. Souies 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.
`
`DISCUSSlON
`
`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 con-
`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 Soules 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?
`
`AUTHOR: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 CR]. No sys-
`tematic evolution 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 436mm Hg line to the extent suffi-
`cient to improve the CHI, and supply enough emission to con-
`tribute to the lumen level, at a relatively low weight percent.
`The Scales and Meier paper ascribes the CHI 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 CR1 cannot fall that low.
`* Westinghouse Electric Corporation, BloomiieldTNew Jersey.
`l The author wishes to acknowledge the help of Dr. T. F. Soules
`for numerous discussions and E. Homonnay for the testing in
`lamps.
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`,
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`Information for authors
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`to the review of the Papers Committee of the IE8.
`
`The JOURNAL OF THE IE8 is published quarterly by the Illuminating Engl-
`neerlng Society of North America. Manuscripts should be sent to the editor,
`345 East nth Street, New York, N. Y. 10017. All manuscripts are subject
`
`JOURNAL OF lESl JANUARY 197'!
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`91
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`LOWES 1021, Page 5
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`ILLUMINATINGg
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`LOWES 1021, Page 6
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`SOCIETY
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`JOURNAL
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`5-7
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`OCT. 1975-
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`JULY 1978
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