US2759119A - Combination light source - Google Patents

Description

ug- 14, 1956 l.. THORINGTON COMBINATION LIGHT SOURCE 2 Sheets-Sheet l Filed sept. 16. A1953 ug- 14, 1956 L.. THoRlNGToN COMBINATION LIGHT souRcE 2 Shee'ts-Sheet 2 Filed Sept. 16, 1953 35 if f Il f fpm-e722 INVENTOR. l//CE 77/0E/A//'0A/ United States Patent COMBINATION LIGHT SOURCE Luke Thorington, Glen Gardner, N. J., assigner to Westinghouse Electric Corporation, East Pittsburgh, Ba., a corporation of Pennsylvania Application September 16, 1953, SerialNo. 380,408

4 Clail11 S (Cl. 313-109) This application is a continuation-in-partof my application Serial No. 55,672, iiled October 21, 1,948, now abandoned, and my application Serial No. 126,506, iiled Nov. 10, 1949.

This invention relates to the color modification of light sources, especially incandescent electric lamps, and to the phosphors used in eiecting this modiiication.

'Ihe principal object of my invention, generallyconsidered, is to make use of the electron emission, as well as the ultra-violet radiation, from the filament of an incandescent electric lamp to act on a phosphor coating on the inner surface of the envelope of such a lamp, in order to produce a worthwhile part of the emitted light by photoluminescence or low-voltage high-current hightemperature cathodoluminescence with or without gas discharge phenomena.

Another object of my invention is to made use of the electron-emission from the filament of an incandescent electric lamp to, even at line voltage, excite an eilicient high temperature phosphor to thereby improve the light source in color and eiiiciency.

A further object of my invention is to produce an incandescent electric lamp containing a coating of phosphor on an inner conductive surface on the envelope thereof, to which coating one side of the powerline is connected, the midpoint of the lament is connected thereto, or a direct-current is applied between the filament and the coating, to cause electrons emitted by the filament to move toward and impinge on the phosphor carried on the inner surface of the envelope.

A still further object of my invention is a lamp, such as described in the preceding paragraph, in Whicha conductive phosphor coating is substituted for the conductive surface coating carrying the phosphor.

An additional object of my invention is to employ manganese-activated zinc uoride as a coating on the inner surface of the envelope of an incandescent electric lamp, to add bright green cathodoluminescence at elevated temperatures to the lamp output, to thereby not only improve the eciency but modify the color of the light output of said lamp.

Another object of my invention is to substitute for the normal tungsten lament of an incandescent lamp, of the character above described, a selective radiator such as a Welsbach mixture or Nernst glower in a quartz bulb.

A further object of my invention is to add gas or vapor to a cathodoluminescent lamp, such as above described, to provide a versatile light source in which gas discharge phenomena may contribute to the output, in addition to the other sources of illumination.

Other objects and advantages of the invention will become apparent as the description proceeds,

Figure 1 is a graph compan'ne thc energy distribution of a tungsten iilament lamp with that weighted by the eye sensibility function.

Figure 2 is an elevational view, with parts in axial section, of an incandescent filament lamp embodying my invention.

2,759, lg Patented Aug- 14, 1956 Figure`V is a view corresponding io Fisurc .2.,l but Showina4 an incandcscentlanicnt lanipof tho. iecctor typo Figure. 4 iS, a view. corion?Ondinel toFignrc 2.. but 'Showing a modification in which thel coating o n the inner Surface oi die cnvclonc. is connected to onoA ond. of. thc iilaincnt- Figure 5. is a. view corresponding to Figure, 4, but showing a modification in which thc coating is con: ncctedAv to the @point of thciilanicnt.,

Figures. 6 and7 are views concsponding. to FiaY 4, ont

Showing inoditicaiions. in which a direct Potential. is. applied between the, inicia... and. one cnil. of. the filament. respectively. and the. pho .onor coating.. in. ordcr. to. liniformly direct the emitted electrons from the. filament to said coating.

Figure Sis a View corresponding to Eis,... 4, but showing a substitution ofi an cicctronjcrnittr. in an inncr quartz or refractory translucent bulb which is, in turn, enclosed in an outer bulb.`

In the present case I am proposing a new lamp, that is, a combination incandescent yand cathodolumine'scent lamp which may also be augmented by gas discharge phenomena or photoluminescehce. 4 l

Most of the energy input of an incandescent light source is wasted as heat, avery diicu'lt form of energy to 17e--v ably improve the light source as a whole, that is, both in color and eiciency.

Onemethod of accomplishing the results desired is to iirst produce a conductive surface on the inside of the lamp envelope. This may be done by using any one of the several transparent conductive coatings which are now available. A cathodolumnescent phosphor which functions at low voltages, and at the operating temperature 0f the bulb or envelope, is then coated over the conducting layer. In one mode of operation, one side of the filamolli iSv connected to the conductive coating or the latter may be connected to the midpoint of the filament, and in still another the midpoint or other portion of the tilae ment has a separate unidirectional potential applied thereto. ln any case, electrons thermally ejected from the lamont are accelerated toward. the phosphor where they impinge and cause the coating to luminesce. It is also. desirable that the coating luminesce under impingement thereon by the ultra-violet radiations generated in the envelope by the filament or other source.'

Another mode of accomplishing the desired end is to coat the inside of the envelope with a phosphor which iS electrically conductive and conncct if as. above, rst eliminating thc Separate transparent conductive coating.

In cach caso thc phosphor dcsirably functions. at. high temperatures and transmits visible .radiafions- The iol: lowingnrc considered the most desirable nfoncrtics of a phosphor for the application non.: disclosed.

1- Tho phosphor should .rcspond to reiativclv low voltage, high current cathode .rev cxcitation 2. It should function at relatively high temperatures.

3. It should eiciently transmit visible radiation.

4. It should be electrically conductive.

5. It should luminesce in the most visually eicient portion of the spectrum, that is, the green.

l discovered that the ordinary orange cathodoluminescence of ZnF2:Mn, while being quenched at elevated temperatures, does at even higher temperatures emit a bright green cathodoluminescence. This phosphor fulfills all the above requirements and, in addition, can be easily evaporated and condensed as a thin clear film. A lamp embodying this phosphor is somewhat analogous to the color-corrected mercury lamp of the parent application, Ser. No. 126,506, previously referred to. That is, it has a phosphor maintained at or near its optimum light-generating temperature. Y

The lamp of this disclosure, however, is also not necessarily limited to phosphors having peak efficiency at elevated temperatures. Neither is it limited to incandescent lamps of the common variety. Fori example, it may be desirable to combine an incandescent selective radiator, such as a Welsbach mixture c-rk Nernst glower, with a phosphor-coated bulb. Itis considered desirable to use a quartz or other high-temperature bulb, for operation of the phosphor coatingat temperatures higher than attainable with ordinary bulbs.

,The possibilities of such a source .are extremely interesting. The highest luminous eciencies reported thus far for the cathodoluminescence process are in the neighborhood of 90 lumens per watt. This is for high voltage excitation of sulfide type phosphors. However, with the proper phosphor there is no fundamental reason why high Yeiciency cannot be attained with low voltage excitation. lt is possible to draw emission currents of about 1/2 ampere from an ordinary 100 watt general service lamp filament. For a potential difference of 100 volts, this would mean 50 watts of available power for conversion into light by cathodoluminescence. For a phosphor of 50 lumens/watt cathodoluminescence efficiency, this would mean 2500 lumens additional light, that is, more than twice the amount of light generated by the filament itself when operating in vacuum.

The efficiency of a tungsten lament in vacuum is about lumens/watt, when all interdependent factors are adjusted to the optimum. The combination efficiency would thus be near 23 lumens per watt, or considerably higher than the gas-filled incandescent lamps and the color would be improved. Assuming higher eiciencies attainable in the phosphor, we may conceiveably reach 40 lumens per watt for such a lamp.

Most cathodoluminescent materials are known to have an effectively dead layer surrounding the individual phosphor crystals. Thus in order to Vactually transfer energy to the active centers of the crystals the electrons must first traverse the dead layer. In so doing,fthey lose a large part of their energy for which no luminescence is emitted. Thus, the electrons must be given suicient energy before impact to not only traverse this dead layer, but to also excite the active centers after traversing the dead layer. The ways in which electrons expend their energy in luminescent materials are as follows:

1. A part is lost as heat in the "dead layer. 2. A part is lost vin ejection of secondary electrons. 3. A part is used to engage the active centers and is transformed and emitted as luminescence;

It is thus seen that a conducting phosphor having active centers on its surface may be activated by very lowenergy electrons. Such a material is ZnF2:Mn; it is very conductive and may be excited by 10 volt electrons. ln addition to a lamp such as above described in which the electron-emitting filament is in a vacuum, I may substitute for said vacuum a gas or vapor to produce a versatile light source embodying all of the methods of generating light heretofore found practical, except that used in photoflash lamps. In other words, with a gasiilled incandescent lamp, the envelope of which is phosphor-coated and connected as before described, l may attain light by not only:

1. lncandescence 2. Luminescence, including both cathodoand photoluminescence, but also by 3. Gas discharge phenomena.

The lamp in its greatest simplicity may take the form of an ordinary incandescent lamp having an inside coating of conductive phosphor, such as manganese-activated zinc uoride, electrically connected to one end, or an intermediate part, of the filament. A small amount of a suitable gas or vapor is introduced so that a'discharge may be maintained between the filament and phosphor coating. The phosphor should be responsive to both the ultra-violet, if any, of the discharge, as well as to low voltage electrons. The mentioned phosphor is excited by ultra-violet radiations having wave-lengths shorter than 2200 A. U., by electrons with energies as low as l0 volts, and its green luminescence is stable at high temperatures.

The presence of a small amount of gaskor vapor in the envelope also Yserves to increase, the total of current available for the cathode-ray excitation of the phosphor. Current limitation of the discharge is efeted by a separate series resistance, by the semi-conductive property of the phosphor coating itself, by a choke orV by another ballasting device. Certain types of discharges are selflimiting. This property would be valuable in a lamp embodying my invention. y

Advantages ofthe combination source would be similar to those previously disclosed forthe incandescentcathodoluminescent vacuum lamp, viz., it would operate in ordinary lamp sockets and would have considerably higher eiiiciency and better color than ordinary incandescent lamps. e

Color and color rendition of the source could be varied widely by changing the phosphor, gas filling, or temperature of the filament. As inthe incandescent-cathodeluminescent vacuum lamp, the incandescent body may preferably be a selective radiator such as thoria; 1% ceria, instead of a tungsten, filament, and the bulb may preferably be of quartz or hard glass.

Referring to the drawing in detail, and first considering Figure 1, there is yshown a curve (a) which represents the energy distribution of a tungsten filament lamp operating at a color temperature of 2854 K. which is the operating temperature of an ordinary watt general service lamp.V Curve (br) is the ysame distribution weighted by the eye sensibility function. Thus, if the total area under curve (a), between ?\=4000 A. U. and 7000 A. U., is proportional to the total visible radiated watts, then the area under curve (b) is proportional to the total lumens. Curve (e) is a plot of the'eye sensibility function used in arriving Vat curve (b) and shows the relative see-ability of the various colorsV of light.

It is apparent that the extremely low etliciency of the tungsten filament light distribution below 5000 A. U. is due to the fact that the energy from the .filament is decreasing rapidly in the range, and also the eye sensibility is decreasing even more rapidly. Of course, it is impossible to change the tungsten lament light distribution without changing its temperature and this is not desirable. However, the actual number of lumens produced by the tungsten radiation below 5000 A. U.-can be varied by shifting this energy to more visibly efficient regions of the spectrum by the process of luminescence.

Considering a conventional 100 watt, A-2l gas-lled tungsten lamp,the following is'true: color temperature=2854 K. Total lumens=1630 (initial) n Per cent of total radiation below 4000 A. AU.- -.163%

Per cent of total radiation below 7500 A. U.= 10.81%

Per cent of radiation in visible=10.65%

Total emitted visible watts (4000-7500 A. U.)=10.65

watts Total emitted u. v. watts (below 4000 A. U.)=.l6 watts Thus the ordinary wasted portion of energy below 4000 A. U. for this lamp amounts to about 1.5% of that emitted; in the visible. If' this energy could be transferred to visible, using a, phosphor such as here disclosed',l or possibly bet-ter still, a phosphor having an emission spectrum comparable with that of zinc silicate.

and a quantum efficiency as good, then an appreciable .8 l09=87 lumens; 87 lumensxquantum el.=73 lumens; 73 lumensXenergy loss=.7 7'3=51 lumens; 51 lumensxabsorption loss=.95 5i=49 lumens. Therefore, the totaI- lumen gai`n=49 lumens, and total lamp elciency is The increase in lumens would amount to about 3% and the overall color of the light would be improved over the bare tungsten filament.

Where highest lumens are desired, regardless of color, it is possible to improve the lumen eiciency by about 11% by utilizing all the radiation below 5070 A. U. to produce luminescence having higher luminosity. One tenth of the lumens of the lamp (163 lumens) under consideration are below- 5070I A. U., but by using a phosphor over 350 lumens could be produced. The total lumens of the source would thenbe 163014-350-1-63: 1817 lumens; the color would be yellowish but not displeasing because of the large excess of red afready present. Phosphors for the above applications are available now, but the diiculty is that they are quite temperaturesensitive and, therefore, would necessitate the use of large cumbersome bulbs. The problem in this respect is the same as for the phosphor-coated HPMV lamp. I therefore, propose lamps such as illustrated in Figs. 1 to 4, inc., of the parent application Serial No. 126,506, previously referred to, but in which an incandescent lilament lamp, having an ultra-violet-transmitting envelope, replaces the HPMV lamp.

In Fig, 2 there is shown an embodiment of my invention in which a phosphor coating 34d is applied' directly to the inner surface of the envelope 22d of an incandescent electric lamp 12d adapted for alternating or directcurrent operation. This lamp may be of otherwise conventional construction; involving a screw-threaded base 21d, a stern 19d, and in incandescible desirably coiled lilament 25d supported on leads 17d and 18d extending therefrom. The filament may be braced by a spud 15d, the normally lower end ofwhich is embedded in a button on the end of an arbor Iextending from the stem 19d. The envelope 22d may be evacuated or contain an inert gas, as desired in accordance with conventional practice.

In this case, the ultra-violet light given off by the lilament, when incandesced, acts on the phosphor coating 34d, resulting in the generation of fluorescent light which correspondingly augments andl modifies the spectrum of the light given by the. filament. The phosphor desirably has a. green-yellow emission and is activated by long and short ultra-violet rays, and a quantum eiciency near .9 or above. Such phosphors as manganese-activated zinc orthogermanate and zinc-activated zinc oxide are examples of suitable phosphors for this application. However, manganese-activated zinc fluoride, although not excited by long ultra-violet rays, is particularly desirable as it operates eliciently at the relatively high temperature of the envelope of an incandescent lamp under electron excitation, thereby making it especially suitable for the applications of Figs. 4 to S, incl.

Referring now to the embodiment of my invention illus- :16.8 l-. p..w.

trated in Fig. 3 there is shown a lamp 12e, also adaptedl for alternating or direct-current operatiomwhich includes an incandescible filament 252. The lamp 12e corresponds generally with the lamp 12d of the preceding embodiment, except that it has a larger and differently-shaped envelope 22?, and a portion thereof is coated with reliectifng material 35, such as, silver or aluminum, to concentrate the light on the remainder of bowl 36 of the envelope, which is coated with liuorescent material 34e. The liuorescent material in this instance may correspond with that of, the preceding embodiment, although because the envelope of this lamp mayoperate at a lower temperature, it need not be such that will operate etiiciently at the relatively high temperature of the lamp of the preceding embodiment. l

Referring now to the embodimentA of my invention illustrated in Fig. 4 there is shown an incandescent electric lamp 12f to be usedy on alternating current only or on direct current in which the right hand end of the incandescible filament 25f, as viewed in said figure, is connected to the negative pole of the supply. It comprises an envelope 22f, based as indicated at 21f and enclosing a stem 19 supporting said lilament. In the present instance, the filament Zf may be formed of tungsten, thoriated' tungsten, or other material having high luminousV eiiiciency and high electron-emissivity. The inner surface of the envelope desirably carries a conductive coating, to which is applied a film or coating of a photo-and cathodoluminescent phosphor. Such conductive coating is desirably a conductive glass or glaze containing tin oxide, examples being those designated by the Pittsburgh Plate Glass Co. trademark Nesa, and the Corning Glass Works trademark EC. As another example, a conductive tin and antimony compound which may be produced as described and claimed in the Mochel Patent No. 2,522,531, may be used. As an alternative the phosphor coating may be mixed with conductive material, if not naturally conducting.

The envelope may be either evacuated or contain inert or rare gas such as nitrogen, argon, neon, krypton, xenon, or mixtures of said gases. The pressure of the gas, if used, i's desirably not high enough to allow a destructive arc discharge across the, lilament.

In order to create an electron ow between the filament and the phosphor during operation, one side of the lilament is connected to the phosphor coating 34f, as by a resilient extension, indicated at 37, from the lead 181, so that during operation the phosphor coating is activated, not only by ultra-violet radiation, but also by an electron discharge thereto. lf used on alternating current, the electron discharge will, of course, only pass to the coating 34f on alternate half cycles, that is, only when the lament 25f is negative with respect thereto.

Fig. 5 shows a lamp 12g, which may be identical with the lamp 12f of Fig. 4, except that it rnay be used on alternating or directcurrent without regard to polarity. In this case the phosphor coating 34g is connected to themidpoint 38 of the filament, as by means of supporting lead 39, as indicated at 37g.

Fig. 6 represents a lamp 12h, which may be like the lamp 12f of Fig. 4, except that it is intended for use on only alternating current. The midpoint 38h of the filament 25h is connected to the negative side or pole of a battery 39, or other source of unidirectional power, which here serves as the force causing electrons to flow to the phosphor coating 34h, as through the intermediate contact or ring 41 of a medium or mogul 3-lite base 2i, which may in this case be used on the lamp instead of a conventional screw-threaded medium base. The positive pole of the source 39 is connected to the phosphor coating 34h on the inner surface of the envelope 22h as by a lead 42 through the envelope neck or in any other suitable manner.

Fig. 7 represents a lamp 12k, which is intended for use on only alternating current. It may be like the lamp 12f of Fig. 4 except that one end of the filament 2Sk is connected to the negative side or pole ofthe battery 39k, Aor other source of unidirectional power. Such. connection may be through the shell of a medium or mogul f3-lite base 21k, which may in this case be used on the lamp instead of a conventional screw-threaded base. The positive pole of the source 319k is connected to the phosphor coating 34k on the inner surface of the envelope 22kas by an auxiliary lead 42k from the intermediate contact or ring 41k of said base, and a resilient contact member 37k extending from said auxiliary lead. This means that during operation of the lamp, electrons are drawn from the filament 25k to the phosphor coating 34k, as in the embodiment of Fig. 6. The only essential difference is that the unidirectional potential is applied between one end, rather than the central portion, of the filament and the phosphor coating.

In the embodiment of Fig. S, a lamp 12m is represented which is intended for use on alternating current only or on direct current in which the top end to the electron-emitter 25m, as viewed in said gure, is connected to the negative pole of the supply. It may be like the lamp lZf of Fig. 4 except that the iilamentary light source is here replaced by the electron-emitter 25m enclosed in an inner quartz bulb 43, or other high-temperature translucent inner envelope, which may be either-evacuated or contain low-pressure fill gas, like the envelope 22 of Fig. 4. The quartz bulb 43 is supported by the leads 17m and lm extending from the stern 19m or in other suitable manner in an outer envelope 22m which outer envelope may be clear of a phosphor coating, and such a coating applied to the inner surface of the quartz envelope 43, as indicated at 34m. However, if desired, the outer envelope 22m may carry the phosphor coating, and the inner envelope be clear, if cathodoluminesence is to be sacriced. If the coating is applied to the inner envelope, there is a contact between it and one side of the electron emitter 25m, as indicatedV at 371,

The size of the phosphor-carrying envelope is, in each embodiment, desirably such that during operation it is maintained at a temperature approximately optimum for the generation of visible light by the phosphor coating. However, such temperature may range between one approximately optimum and one higher or lower to allow for selection of `a convenient bulb, that is, avoid undesirably large or small envelope size.

Although preferred embodiments have been disclosed, it will be understood that modications may be made within the spirit and scope of the invention.

l claim:

1. In combination, a power-operable incandescible source of radiant energy including ultraviolet radiations and electrons, a light-transmitting envelope surrounding said source, a light-transmitting coating on the inner surface of said envelope comprising a phosphor-including electrically-conductive coating having an efiicient output .at the normal envelope operating temperatures and for which production of light in the green region of the spectrum is high upon impingement of said coating by radiant energy and electrons emanated from said source when operated, means electrically connecting said coating to said source, said source When operated producing visible radiations amounting to a substantial portion of the total visible radiations produced by said source and said phosphor, whereby the visible light from said source is augmented and the color thereof modiied by the light generated by said phosphor.

2. In combination, a. power-operable incandescible source of radiant energy including ultraviolet radiations and electrons, a light-transmitting envelope surrounding said source, a light-transmitting coating on the inner surface of said envelope comprising a phosphor-including electrically-conductive coating havingan eicient output at the normal envelope operating temperatures and for which productionV of light in the green region of the spectrum is high upon impingement of said coating by radiant energy and electrons emanated'from said source when op-l erated, means for applying 'a potential between said coating and said source so thatelectrons emitted by said source during operation will be drawn to said coating, said source when operated producing visible radiations amounting to a substantial portion of the total visible radiations produced by said source' and said phosphor, whereby the visible light from said source is augmented and the color thereof modified by the light generated by said phosphor.

3. ln combination, a power-operable incandescible source of radiant energyv including ultraviolet radiations and electrons, a light-transmittingenvelope surrounding said source, a light-transmitting coating on the inner surface of slaid envelope comprising aphosphor-including electrically-conductive coating for which production of light in the green region of the spectrum at the normal envelope operating temperatures is high upon impingement of said coating by radiant energy and electrons emanated from said source when operated, said phosphor being one of the group consisting of manganese-activated zinc uoride, manganese-activated zinc orthogerr'nanate,4

and zinc-activated zinc oxide, means electrically connecting said coating to said source, said source when operated producing visible radiations amounting to a substantial portion of the total visible radiations produced by said source and said phosphor, whereby the visible light from said source is augmented and the color thereof modified by the light generated by said phosphor.

4. In combination, a power-operable incandescible source of radiant energy including ultraviolet radiations and electrons, a light-transmitting envelope surrounding said source, a light-transmitting coating on the inner surface of said envelope comprising a phosphor-including electrically-conductive coating having an eicient output at elevated temperatures and for which production of light in the green region of the spectrum at the normal envelope operating temperatures is high upon impingement of said coating by radiant energy and electrons emanated from said source when operated, the size of said envelope being such that during operation it is maintained at a temperature between one approximately optimum for the generation of visible light by radiations and electrons impinging on said phosphor and one only higher to avoid undesirably large envelope size, means electrically connecting said coating to said source, said source when operated producing visible radiations amounting to a substantial portion of the total visible radiations produced by said source and said phosphor, whereby the visible light from said source is augmented and the color thereof modified by the light generated by said phosphor.

References Cited rin the` file of this patent UNITED STATES PATENTS 1,275,890 Flannery et al.,v Aug. 13, 1918 2,177,705 Friederich Oct. 31, 1939 2,654,042 ClarkeV et al. Sept. 29, 1953

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