United States Patent (19]
`Patton et al.
`
`lllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll 111111111111
`US005118985A
`5,118,985
`[11] Patent Number:
`[45] Date of Patent:
`Jun.2, 1992
`
`[54] FLUORESCEST Il'<CANDESCEST LAMP
`[75]
`Inventors: Robert J. Patton, Acton; Kailash C.
`Mishra, Chelmsford; Ernest A. Dale,
`Hamilton; Costas Lagos, Danvers, all
`of Mass.
`[73] Assignee: GTE Products Corporation, Danvers,
`Mass.
`
`[21] Appl. No.: 727,299
`[22] Filed:
`Jul. 9, 1991
`
`[63]
`
`Related U.S. Application Data
`Continuation of Ser. No. 458,923. Dec. 29, 1989, aban(cid:173)
`doned.
`
`Int. Cl.~ ............................................... HOlK 1/32
`[51]
`[52] U.S. Cl. .................................... 313/485; 313/487;
`313/578; 313/315
`[58] FieldofSearch ................. 313/25,112.113,465,
`313/483,485, 502,487, 161. 578. 491; 315/248,
`109.3: 372/80; 346/110 R
`References Cited
`U.S. PATENT DOCUMEKTS
`2.405.26 I 8/1946 Levi et al. ........................... 313/112
`2.759.119 8/1956 Thorington ..................... 313/578 X
`3.947.719 3/1976 Ott .................................. 313/11:! X
`
`[56)
`
`4,097.776 6/1978 Allinikov ............................ 313/502
`4.645.290 2/1987 Walsh ............................. 313/112 X
`4.727,283 2/1988 Van Kemenade et al. ......... 313/487
`
`FOREIGN PATENT DOCUMENTS
`0027334 4/1981 European Pat. Off ............. 313/112
`0147677 11/1979 Japan ................................... 313/112
`
`Primary Examiner-Donald J. Yusko
`Assistant Examiner-Ashok Patel
`Attorney, Agent, or Firm-Martha Ann Finnegan;
`Robert E. Walter
`
`ABSTRACT
`(57]
`An incandescent lamp is provided with a phosphor
`coating on its lamp envelope. The phosphor coating
`alters the spectral distribution of radiation emitted by
`the lamp and acts as a diffuser. In one embodiment, the
`phosphor coating absorbs radiation at wavelengths
`below 500 nanometers and emits radiation at wave(cid:173)
`lengths above 500 nanometers to provide an improved
`bugfoiler lamp. In another embodiment. the phosphor
`coating absorbs radiation in the ultraviolet. violet and
`blue wavelength range and emits radiation at longer
`wavelengths that more effectively stimulate the human
`eye.
`
`1 Claim, 4 Drawing Sheets
`
`12
`
`22
`
`Vizio EX1027 Page 0001
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`

`
`U.S. Patent
`
`June 2, 1992
`
`Sheet 1 of 4
`
`5,118,985
`
`12
`
`22
`
`FIG. I
`
`Vizio EX1027 Page 0002
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`

`
`U.S. Patent
`
`June 2, 1992
`
`Sheet 2 of 4
`
`5,118,985
`
`0.30
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`X
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`VI -
`
`EXCITATION SPECTRUM
`FOR YAG: Ct FSS1-15
`
`~EMISS=
`S25nm
`
`0.00 L----L-~-~-'-----'--~--L---.&----1.---'--.......__~
`250
`200
`300
`350
`450
`500
`400
`
`WAVELENGTH (nm)
`
`FIG. 2
`
`Vizio EX1027 Page 0003
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`

`
`U.S. Patent
`
`June 2, 1992
`
`Sheet 3 of 4
`
`5,118,985
`
`3.00
`
`2.75
`
`2.50
`
`CORRECTED VISIBLE EMISSION
`FROM YAG: Ce FSS1-15
`}.EXC = 456nm
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`-c
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`~ 1.75
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`480
`500
`520
`540 560
`580 600 620
`640 660
`WAVELENGTH (nm)
`
`FIG.3
`
`Vizio EX1027 Page 0004
`
`

`
`U.S. Patent
`
`June 2, 1992
`
`Sheet 4 of 4
`
`5,118,985
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`WATTS I NANOMETERS
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`Vizio EX1027 Page 0005
`
`

`
`1
`
`FLUORESCEST ISCASDESCEST LAMP
`
`5,118,985
`
`2
`phosphor coating alters the spectral distribution of radi(cid:173)
`ation emitted by the lamp.
`In one embodiment of the invention. the phosphor
`coating absorbs radiation in a wavelength range includ(cid:173)
`ing ultraviolet. violet and blue radiation and emits visi(cid:173)
`ble radiation in a longer wavelength range that more
`effectively stimulates the human eye.
`According to another embodiment of the invention,
`the phosphor coating is selected to absorb visible radia-
`10 tion in a wavelength range below 500 nanometers and
`to emit radiation in a wavelength range above 500 nano(cid:173)
`meters so that the lamp is poorly seen by insects during
`operation. The lamp having a phosphor coating can
`provide a nontoxic bugfoiler lamp depending on the
`phosphor used.
`The phosphor coating is disposed on an inside surface
`of the lamp envelope and preferably has sufficient thick(cid:173)
`ness to diffuse radiation emitted by the filament. Pre(cid:173)
`ferred phosphor coatings include yttrium aluminum
`garnet doped with cerium (YAG:Ce), lithium titanate
`doped with manganese (Li2Ti03:Mn) and combinations
`thereof.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`For a better understanding of the present invention,
`together with other and further objects, advantage~ and
`capabilities thereof. reference is made to the accompa(cid:173)
`nying drawings which are incorporated herein by refer(cid:173)
`ence and in which:
`FIG. I is a cross sectional elevational view of an
`incandescent lamp in accordance with the invention;
`FIG. 2 is a graph which illustrates the excitation
`spectrum of a preferred phosphor coating:
`FIG. 3 is a graph which illustrates the emission spec(cid:173)
`trum of the phosphor coating of FIG. 2; and
`FIG. 4 is a graph which illustrates the spectral power
`distribution of an incandescent lamp having a phosphor
`coating of the type shown in FIGS. 2 and 3, for various
`filament temperatures.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`A cross-sectional view of an incandescent lamp incor(cid:173)
`porating the present invention is shown in FIG. 1. A
`tungsten filament 10 is mounted within a glass envelope
`12. The filament 10 is mechanically supported within
`the envelope by electrical leads 14 and 16. The electri(cid:173)
`cal leads 14 and 16 extend through a lamp stem 18 to a
`lamp base 20. A luminescent phosphor coating 22 is
`disposed on the inside surface of lamp envelope 12.
`The function of the luminescent phosphor coating is
`to absorb radiation from filament 10 in a first wave(cid:173)
`length range and to emit radiation in a second wave(cid:173)
`length range. Thus, the phosphor coating alters the
`spectral distribution of the radiation emitted by the
`lamp. The phosphor coating 22 preferably diffuses light
`passing through envelope 12 so that the filament 10 is
`not visible through envelope 12 during operation.
`In one preferred embodiment of the invention, the
`phosphor coating 22 increases the efficacy of the lamp
`relative to incandescent lamps not having a phosphor
`coating. It is known that the human eye is much less
`sensitive to radiation in the blue and violet portions of
`the visible spectrum than to radiation in the yellow and
`green portions of the visible spectrum. In order to im(cid:173)
`prove the luminous efficacy of the lamp, a phosphor
`coating 22 which absorbs radiation in a portion of the
`spectrum including ultraviolet, violet and blue wave-
`
`This is a continuation of copending application Ser.
`No. 07/458,923, filed on Dec. 29, 1989, no~· abandoned. 5
`
`FIELD OF THE INVENTION
`This invention relates to incandescent electric lamps
`and, more particularly, to incandescent lamps which
`have a luminescent phosphor coating on the lamp enve(cid:173)
`lope to alter the spectral distribution of the radiation
`emitted by the lamp.
`
`BACKGROUND OF THE INVENTION
`Soft white incandescent lamps utilize a clear glass 15
`lamp envelope which has been coated with a fine trans(cid:173)
`parent powder, usually silica, on its inside wall. The
`powder diffuses the light from the filament so that the
`eye cannot form a focused image of the filament. The
`silica powder does not alter the spectrum of the light 20
`emitted from the filament. Some light is lost due to
`reverse scattering by the silica powder.
`Lamps known as "bugfoiler" lamps emit radiation in
`a range of wavelengths which is poorly seen by many
`insects. Prior art bugfoiler lamps have utilized a cad- 25
`mium sulfide coating on the lamp envelope. The cad(cid:173)
`mium sulfide acts as a filter and attenuates wavelengths
`less than 500 nanometers more than wavelengths above
`500 nanometers. Consequently, the radiation emitted by
`the lamp is primarily in a wavelength range above 500
`nanometers. Such bugfoiler lamps are relatively ineffi(cid:173)
`cient, since the shorter wavelengths are unused. In addi(cid:173)
`tion. the cadmium sulfide coating is toxic.
`The human eye is much more sensitive to wave- 35
`lengths in the yellow portion of the spectrum than to
`wavelengths in the violet and blue portions of the spec(cid:173)
`trum. Thus. radiation emitted by an incandescent lamp
`in ultraviolet, violet and blue portions of the spectrum
`produces very little stimulation of the human eye.
`Luminescent phosphors are widely used in fluores(cid:173)
`cent lamps to convert ultraviolet radiation to visible
`radiation. The phosphor is a coating on the lamp enve(cid:173)
`lope. The phosphor absorbs radiation in one wave(cid:173)
`length range and emits radiation in another wavelength 45
`range. To our knowledge, luminescent phosphors have
`not been used on incandescent lamps.
`It is a general object of the present invention to pro(cid:173)
`vide improved incandescent lamps.
`It is another object of the present invention to pro- so
`vide an incandescent lamp having a luminescent phos(cid:173)
`phor coating to alter the spectral distribution of radia(cid:173)
`tion emitted by the lamp.
`It is a further object of the present invention to pro(cid:173)
`vide incandescent lamps having high luminous efficacy. ss
`It is yet another object of the present invention to
`provide improved lamps that are poorly seen by insects.
`
`30
`
`40
`
`SUMMARY OF THE INVENTION
`According to the present invention, these and other 60
`objects and advantages are achieved in an incandescent
`lamp comprising a light transmissive envelope, a fila(cid:173)
`ment mounted within the envelope, means for coupling
`electrical energy to the filament, and a luminescent
`phosphor coating on a surface of the envelope, the 6S
`phosphor coating being selected to absorb radiation
`from the filament in a first wavelength range and to
`emit radiation in a second wavelength range so that the
`
`Vizio EX1027 Page 0006
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`

`
`5,118,985
`
`3
`lengths is utilized. The phosphor coating 22 is selected
`to emit radiation in a portion of the visible spectrum
`where the human eye is highly sensitive. The phosphor
`coating converts ultraviolet radiation and radiation at
`the low end of the visible spectrum to longer wave- 5
`length radiation that is more useful for illumination.
`According to another aspect of the invention, the
`phosphor coating 22 is used to provide an improved
`bugfoiler lamp which is poorly seen by many insects. It
`is known that radiation at wavelengths above about 500 10
`nanometers is poorly seen by many insects and that
`lamps having radiation limited to wavelengths above
`500 nanometers do not attract insects. The phosphor
`coating 22 is selected such that wavelengths in a range
`below 500 nanometers are absorbed by phosphor coat- 15
`ing 22, and radiation in a wavelength range above 500
`nanometers is emitted by the phosphor coating. The
`phosphor coating 22 improves the operating efficiency
`of a bugfoiler lamp since radiation at wavelengths less
`than 500 nanometers is converted to useful radiation 20
`above 500 nanometers rather than being attenuated by a
`filter. In addition, the bugfoiler lamp with phosphor
`coating 22 can provide a nontoxic lamp, depending the
`the phosphor used.
`The phosphor coating 22 can be applied to the inside 25
`surface of lamp envelope 12 using conventional electro(cid:173)
`static coating techniques. Alternatively, the phosphor
`material can be dispersed in an organic lacquer and
`applied as a coating on the inside surface of envelope 12.
`Then the envelope 12 is placed in an oven, and the 30
`lacquer is baked off, leaving a phosphor coating on the
`glass surface.
`One preferred phosphor coating is yttrium aluminum
`garnet doped with cerium (YAG:Ce). The excitation
`spectrum of YAG:Ce is shown in FIG. 2 where the 35
`relative excitation efficiency is plotted as a function of
`wavelength for a wavelength range of 225 nanometers
`to 500 nanometers. It is seen from FIG. 2 that the maxi(cid:173)
`mum absorption of YAG:Ce occurs at 456 nanometers.
`The emission spectrum of Y AG:Ce when stimulated 40
`with radiation at 456 nanometers is shown in FIG. 3 in
`which output power is plotted as a function of wave(cid:173)
`length. A major portion of the emitted radiation is in a
`wavelength range above 500 nanometers.
`Another suitable phosphor coating is lithium titanate 45
`doped with manganese (Li2Ti03:Mn). Lithium titanate
`doped with manganese can be used alone or in a mixture
`with Y AG:Ce to produce a desired output spectrum.
`Lithium titanate doped with manganese has a broad
`excitation spectrum in a range of about 300-500 nano- 50
`meters and a maximum in its emission spectrum at about
`640 nanometers. Other suitable phosphors include most
`luminescent phosphors which are activated by a manga(cid:173)
`nese in the +4 valence state, and zinc sulfide doped
`with copper and manganese.
`Spectral power distribution curves for a 200 watt
`incandescent lamp having a Y AG:Ce phosphor coating
`
`55
`
`4
`are shown in FIG. 4 wherein watts per nanometer emit(cid:173)
`ted are plotted as a function of wavelength. Curves 40,
`42 and 44 demonstrate the spectral performance for
`filament temperatures of 2800' K., 3000' K. and 3200'
`K .. respectively. The corresponding lumen outputs are
`3037, 5736 and 8281 lumens, respectively. The lamp
`represented by FIG. 4 provides about 70% more light
`output than prior art bugfoiler lamps. It is seen from
`FIG. 4 that very little radiation is emitted by the lamp at
`wavelengths less than 500 nanometers.
`With reference to FIG. 4, it is noted that a lamp
`having a Y AG:Ce phosphor coating has some output in
`a wavelength range of about 400 nanometers. In addi(cid:173)
`tion, the lamp output reaches a minimum at a wave(cid:173)
`length somewhat below 500 nanometers. Thus, the
`lamp may be somewhat visible to insects. By using a
`phosphor coating comprising a mixture of Y AG:Ce and
`Li:TiOa:Mn, the lamp output at about 400 nanometers
`is eliminated and the entire spectral curve is shifted to
`the right (longer wavelengths), thus providing a lamp
`that is less visible to insects. However, the addition of
`Lb TiOa:Mn reduces the lumen output of the lamp. A
`desired spectrum and lumen output can be obtained by
`a selected ratio of YAG:Ce and Lh TiOa:Mn.
`While there have been shown and described what are
`at present considered the preferred embodiments of the
`present invention, it will be obvious to those skilled in
`the art that various changes and modifications may be
`made therein without departing from the scope of the
`invention as defined by the appended claims.
`What is claimed is:
`1. An incandescent lamp comprising:
`a light-transmissive envelope;
`a filament mounted within said envelope;
`means for coupling electrical energy to said filament;
`and
`a luminescent phosphor coating on a surface of said
`envelope, said phosphor coating being selected to
`absorb radiation from said filament in a first wave(cid:173)
`length range including ultraviolet, violet and blur
`radiation and to emit visible radiation in a second
`wavelength range having wavelengths longer than
`wavelengths in said first wavelength range, said
`phosphor coating consisting of a mixture of
`YAG:Ce phosphor and Li2Ti03:Mn phosphor,
`said Li2Ti03:Mn phosphor having manganese in
`the +4 valence state and a maximum in emission
`spectrum at about 640 nanometers, said mixture
`comprising a sufficient amount of Li2Ti03:Mn
`phosphor for shifting the spectral output wherein
`substantially no spectral output is present at about
`400 nanometers and below about 500 nanometers
`so that the lamp output is poorly seen by insects
`during operation.
`•
`
`• * •
`
`•
`
`60
`
`65
`
`Vizio EX1027 Page 0007