US2654043A - Discharge lamp, method of operating, and method of making - Google Patents

Description

Sept- 29, 1953 G. A. FREEMAN Erm. 2,554,043

DISCHARGE LAMP, METHOD OF OPERATING, AND METHOD 0F' MAKING Filed Feb. 27, -1948 *171 ZZ '29.1. 7km-Giel m i ZN\\\ a /o 2b so 4o 0 /W vd 300 77M! /A/ Harmful/V06 NVENTORS G. fr. resi/14M C? 6. mwa-zsm, fr.

40 no Nm kunwr ffm/ the: ATTORNEY Patented Sept'. 29, 1953 DISCHARGE LAMP,i METHOD# OPERAT- ING,.AND METHOD OF MAKING George A. Freeman, East Orange, and Carl G. Anderson, Jr., Packanack'Lake, N. J., assignors to. Westinghousev Electric Corporatinmlttssburgh, Pag. a corporationof: Pemisylvala` Application February 27, 1948Serial No. 11,714'

7 Claims. l

This invention relatesto discharge lamps and more particularly to such which may furnish instantaneous flashes of light of high intensity.

The principal object of our invention, generally considered, is to provide a durable lamp which efficiently emits intense-flashes of light at'Y desired time intervals.

Another object of our invention is to provide a discharge lamp, the envelope of which has a fused quartz tubular portion unitedfat its ends to electrode-containing glass chambers which serve to collect quartz powder vaporized during operation.

A further object of our invention is to provide a discharge lamp adapted to emit intense flashes or light and which comprises an intermediate fused'quartz'tubular envelope portion and metal terminals holding inwardly-extending tungsten electrodes at each end thereof, said metal ter--v minals being connected to the respective ends of said tube by graded seal portions forming-end chambers large enough to cushion thesudden expansion ofl gas in the tube during a flash.

A still further object of our invention' is to operate a lamp such as above rdescrilavedathigher than usual power to thereby avoid blackening and improve the operation in general.

A-n additional object of our invention is to initiate the operation of a discharge lamp, such as above described, by the employment of atrigger having a plurality of loops disposed around the quartz tubular portion to thereby avoid inconsistent firing.

Other objects and advantages of the invention will become apparent as the description pro'- ceeds.

Referring to the drawing:

Figure l is an axial sectional view to scale of a lamp embodying our invention with parts shown in elevation, and an operating circuit indicated diagrammatically.

Figure 2 is a graph illustrating typical relations between light intensity and duration of flash :from a lamp embodying our invention.

Figure 3 is a graph illustrating how certain of the characteristics, such as the output in lumens per watt, the peak lumens, the duration of the flash above one third of the peak, and the lumen seconds output, vary with the energy in each ash in terms of watt seconds, fora lamp embodying our invention.

Figure 4 is a graph showing the spectrum distribution of the light from a lamp embodying our invention.

Figure 5 is a graph comparing the light output 2 and the duration ofthe flash for a lamp` embodying our invention with those of a standard photographic flash' tube, when the input of each is 48` wattl seconds-per flash.

A 'new flashing-lamp has been developed especially for safe landing of aircraft under all weather conditions.y Instrument flying brings a plane closeto the airport where a new lighting system using lamps according to our invention provides the pilot the assurance that only direct visionI can give f as to the runway location.

Tests conducted during the war have shown that alight can'p'enetrateV useful distances in dense fog, providinglextremelyliigh candlepower isused. Thelnew 'light source, ten 'times the suns brightness, has been'combinedwith a large parabolic reflector to-concentrate more than three billion candlepower lin anarrow beamtoobtain the required fog penetration. Thirty-six such units are installed lat ground'level, spaced in a lin-e 3200 feet long, to Aguide-apilot down to the airport runway.

Flashing lightv was selected'as the only means of obtaining 'therequired'intensity and still not blind the'pilot as'he" approached'more closely. Only a i'ewvvatt'sV average power is used by a flashing'lamp butth-ervpeak power in the flash isv millionsof watts. Extreme light intensity is produced, lasting' a fewz millionths of a second. Suchla lamp is-operatfed-frcm energy accumulated in a condenser'whichis released at the desired A'instant by 'means'of an ignition spark applied `tothe-lmnp. Before ignition, the lamp is non-conducting. A- hi-gh voltage spark, similar to vautomobile ignition, ionizesthe gas inthe lamp causing -its'ri-'zsistance to suddenly drop from neaninnityto less than one ohm, discharging the'condenseralmos-tinstantly. The intensity of light, eventhough ofvery shortv duration, is many times greater than is `obtainable' from a continuously lburninglamp; 'I'he'series of flashes is repeated 40 times perv minute to keep the `pilot informed 'ofthe' location of the runway until the landing*ismade` y -In determining the proper flashing lamp design; commercial photographicfl-ash tubes were considered first. The rapidly repeating Vflash requirement wasfound toshorten lamp life exeessively unless"veryflowv energy per flash was used. Low flash energy was found to result in very low lamp emciency. A more rugged flashing lamp` wasrequired that also had the maximum possible light' intensity.v i

'I'heflasnlng lamp 'that was-finally developed vis lsl'iowniin-ligurel yFusedquartz is used :and

special provision made to collect vaporized quartz powder where it will not obstruct t-he light output. The central portion of the lamp is a tough vitreous tube, thick-walled to insure long life, about two inches long and about one fifth of an inch inside diameter. A graded seal is employed at each end to hermetically seal the low thermal expansion quartz to the higher thermal expansion metal terminals. The graded seals have larger diameter than the quartz tube and form end cavities which act as shock absorbers for the sudden expansion of gas during a flash. The vaporized quartz powder is blown into the end cavities where it is harmless since there it cannot absorb light output. As the lamp is used, the thick quartz wall gradually wears away on the inside until eventual break-through causes the lamp to fail.

The new flashing lamp has been standardized as with a rating of about 50 Watt seconds per flash when operated at 40 flashes per minute. The power is supplied from a 2000 volt charge on a 25 microfarad condenser. The rate of energy consumption during the flash is obtained by dividing the energy per flash by the flash duration and is found to be 3,000,000 Watts. obtained by dividing the output in a direction perpendicular to the lamp axis by the size of the light source viewed from the same direction, and is found to be 10,000,000 candlepower per square inch.

The flash current is calculated using the formula for the discharge of condenser T=RC. Since C is made 25 microfarads and T is measured to be 17 microseconds, R is found to be .68 ohm.

With 2000 volts applied to .68 ohm, the peak current estimated by Ohms law is 2940 amperes. The average power used in the lamp is obtained by dividing the energy per flash by the interval between flashes and is found to be only 33 watts.

Krypton gas is used in the lamp to obtain the maximum light efficiency. Argon gas will give about 80% as much light and nitrogen still less.

Referring to the drawing in detail, like parts being designated by like reference characters, there is shown in Figure 1 a lamp embodying our invention and comprising :an envelope I I with an intermediate tubular portion I2, preferably formed of tough transparent vitreous material such as fused quartz, fused magnesia, fused alumina, or similar refractory material. In a preferred embodiment, the intermediate portion I2 is about 2" long, has an inside diameter of about 4 millimeters or 1/5", and a wall thickness of about 3 millimeters. The envelope II holds a pair of electrodes I3 and I4 desirably formed of tungsten, molybdenum or similar refractory or -high melting point metal. In a preferred form, they consist of relatively heavy solid or non-tubular, as distinguished from hollow, tungsten cylinders, that is such about 1/8 in diameter that is, nearly as large as the bore of the portion I2, and about 1% long, presenting to one another flat faces relatively large in area. These electrodes are disposed in end chambers I5 and I6, respectively extending from opposite ends of the quartz tubular portion I2. The end chambers are formed as graded seals, desirably hermetically sealed to the quartz tube after first beading the ends of the latter with rings of special flux glass I1, using a glass lathe.

The graded seal portions forming the end chambers I5 and I6 may be sealed directly to the electrodes I3 and I4, respectively. Preferably, each electrode has its outer end portion fitting in an end cup or cap I8 or I9, and the caps are in The brightness is turn sealed to the respective ends of the graded seal portions I5 and I6. The cups I8 and I9 are desirably formed of material which seals well to the glass of the end chamber members I5 and I6. For that purpose, they may be formed of Kovar as defined in the Lempert et al. Patent No. 2,279,831, dated April 14, 1942, or other suitable metal. Such cups are desirably degreased, baked in humid hydrogen, the tungsten electrodes chamfered at their outer ends, then degreased and spot welded to the Kovar cups. Rings of brazing wire are then formed, degreased, and two rings applied over each electrode. A boat is used to hold each electrode assembly in a vertical position with the Kovar cup down. Heating in a humid hydrogen atmosphere at about 1010 C. for about 20 minutes serves to braze each electrode to its cup, thereby making a good electrical connection therebetween.

Before securing the cup to the corresponding end chamber member, its edge is desirably rst glassed, as on a lathe, oxidation removed as in a hot anodic alkaline electrocleaner, the parts rinsed in clean water, neutralized, again rinsed, and then dried.

An `assembled electrode and cup is secured to its graded seal and the latter to the quartz tube, preferably in the following manner. A graded seal with a protective ring of asbestos ribbon around its end is held in a lathe head chuck and la quartz tube with one end plugged with asbestos is held in the tail chuck. The adjacent ends of the parts are sealed, care being taken to avoid sealing to an unfluxed part of the quartz tube.

The tail chuck is disengaged and the yasbestos plug removed from the quartz tube. The second graded seal, with one end corked and with a protective ring of asbestos ribbon around the end, is placed in the tail chuck and a second seal made as before.

The tail chuck is disengaged and the cork removed from the graded seal. An electrode assembly is placed in the tail chuck and sealed to a graded seal, care being taken that the electrode is not oxidized. A hole may be blown for the exhaust tubulation and an exhaust tube sealed thereabout. The tail chuck is disengaged and the exhaust tube may be bent around so it can be engaged in the tail chuck, care being taken that the exhaust tubulation is disposed axially of the assembled lamp part. The graded seal is desirably annealed while the exhaust tube is being held by the tail chuck.

The assembly is removed, turned around and put into the head chuck, where it is held by the exhaust tubulation, and an electrode assembly is placed in the tail chuck, sealed to the graded seal and annealed, completing the assembly.

The complete assembly is then desirably connected to a vacuum pump and tested for leaks with a spark coil. rlhe lamp is then exhausted, baked, and then filled with an inert gas such as argon or nitrogen at a pressure of about millimeters and tested by flashing two minutes at three flashes per second, using a 24 microfarad condenser charged to about 2000 volts. The polarity is reversed and this is repeated. Triggering is accomplished with the spark coil applied to the center of the quartz tubing. The lamp is then reevacuated and lled with krypton gas to a pressure of about 325 millimeters. The lamp is then preferably flashed for about two minutes at about 40 flashes per minutes on 24 microfarad condenser with a potential of 2000 volts. The

lamp .is then .tippedoff carebeing staken; taavoidl strainin the graded sealsi In order. to `avoid inconsistent firing-duringuse,` bit-.getting more complete gasf.ionization,V weide. sirably. employ a trigger-2|, desirably formed of. suitable wire such as 1'5A `mil-spring1 steel.l orf/nickel"y and wound several times .-a-roun:l:the-quai-tz.-ti-xbe. I2, as illustrated, an intermediate portion there-i of, between end portions whichfencirclethetube, being connected to the timing, mechanism indie.. cated at 22a; For flashing, the-lampi'siconnectedt through a resistance2-3'1 to a.source-.ofdirect current 24, in parallel witha-condenser-2'5`- The new lamp above .described avoids: the-use; of an outer bulb andl vaporizediquartzcollected; in a way to obscure the light. output.- Natural:f cooling of the lamp isthusA not impeded.A llin-Vm largedI or relatively largeend chambers L and- Is.4 serve to collectv the.` vaporizedouartz, sinceithee rapid expansion ofgas duringaflash blowsiwhat.-m everis. vaporizedintofthernf. Thisl has. been found to .worlcoutioluite-y well lin practice, evenwith'loade. ings higher-than 20; wattsaverage... Nostarting. electrode sealis. needed', sinceit hasbeenfound. that a wire, such as' indicated at. 2|-, wrappedV aroundthe quartz tube.-portion I21at the.4 center. of the lamp servesas. well.'` Thenewelamplends.v itself toy forced coolingfor higher load-ings:.b:et.` ter than anyV previously employed.- 'Ihe-.employ.. ment7 of Kovar` cups, such -as .indicated at I Brand I9;A ratherv than glassfares connected.directly-to the` tungsten'electrodes, has avoided'considerable.;y shrinkage sdue to cracking, of fthe. glass'. dares-.

The lamp of ourinvention was rst testedfat20 to..30 watt secondsper flashfrom` 40 to 8041er4 minute. After 10 to. .20: hoursthevarious. lamps.r testedalldeveloped somev blackening obscuringf.y the. light Aoutput and voltagel .breakdown became. high sol that triggering waslinconsistent.. We.. thereforestepped up the. power. per -flaslbto- 3.81 wattseconds and later to` 5.0fandreven as .highvasr 325. Contrary. to. expectations, the. operation .aty higherloading gavelexcellent' results. Blackening. Wasnot only` avoided, but blachened'-larxxpsivvould. become. clean. by raising.- the power perflashz. Then.: voltage .break-down became moreconsistent,and.-4 lamps which had becomehard to startwere made tol start wellagainby4 operating; fori as whileat higher power per ash'.

Examination of. dissected; g lamps; showed that; silica powderv collected in .a-,hardfthick layer;` on the electrodesl When.l run at :low pQWel? .per :flashs the electrodes `coated over completelyfand the; starting voltage became-highka, Whenfrungat/h f, power per flash, the tip off-the,electrogigawouldL` y 55 cleaned, oir or lkept clean, while.powder,stillr e=. Inained onv the .electrode backgof thetip, where.v it did no` harm. Examination oi the. quartz. inter mediate tubeshowedl thatl the inside diameter was increasing with lamp operation due tothe evaporation ofthe quartz atthe high loadings. v ItisA obvious that any incipient black deposit`v is removed-by the evaporation of`l thequartz which is blown into the ends of a lamp around theeleetrodes.

Figure 2` shows the characteristics .of` the, lamp)-h of ourV invention4 with; changesV in thee.capacity, of the condenser 25.- Witlra condenser/ofv 121 microfarad capacity; it will be ,seenY that vlpeakgin-e.. tensity of the flash is only; aboutY 3 1 millions lumens as indicated by the graphe-26,;y When-Itho.. condenser capacityis doubled, the peak lumens increased-to kmillion,asindicated by the graph 2'I. When tripled, it increases to '74 million, as indicated bythe graph. 28. Whenlthe condenser 75 is.-.increased=to 60' microfarads, the-peaky intensity; is 100.8 million lumens, as indicated by the graph Figure 3i shows. othencharacteristicsof the lamp ,of-.ourfinventi'on In-terms of vvattiseconds` per'. ash, the-lumens. per watt increaseA along the curve 31|, the-.peak lumensincrease along the curve` 32;. the duration ofthe flashabove.- 1/3 peak in-Y creasesralong'the: curve 33, whilefthe lumen see-- i ondsioutputz varies .in accordance withv the. curven curve 31f'of a standard photographic ash lamp,

having; anfinput of -48 watt-seconds. Bystandardvphotographic flash lamp, we mean one of theftype designated IPT-14 by Harold Edgertony in'his: article entitled Photographic use of Elec--v trical Discharge Fla-shtubes, Abeg-inning on page 3,90" of ;volume 36, No. 7,. Journal of the. Optical- Societyfof America,.July, 1946; anddescribed by E.- Carlson and D. A.v Pritchard in their article entitled The Characteristics and Application of FlashtubesIl presented at the; Annual Convention of fthe Illuminating Engineering.. Society, Quebec, Canada, September 18 to20, 1946.

Theash tube of'l this invention has: a shorter duration and.y higherT peak output than other known photographic-flash lamps,v as graphically disclosed rFigure5becauseashort arc gap witharelatively highl gas pressure is provided thaty will `have lower resistance-` to the flash current thana long.- straight or coiled discharge. tube; in which thefgask pressure is quite low. The. same.` quantity of energy` is ,usedup faster in thefl'amp offzthis invention. As a result, the hash does not. last as long andthe intensityof thelight, beingI proportional to'thevrate of much higher.

Although preferred embodiments of .our invention. have been disclosed, it will; beunderstood thatmodications may be made withinV the spirit:

and scopeof. the appended claims.. For-example, although krypton gas is .specied as preferred, yetgas containing a `rrnajor proportion ofrkrypton, say saft'y 10% gives, an output approximating that when purekrypton iskused.. Other rare or noble gases, such as argon, xenon, neon, helium, or` mixtures,`may be employed if4 the corresponding,

variations in Ioutput are permissible. The effect,

of pressure, of krypton, forexample, yon. light efflciency was foundl to be relatively unimportant, soA that the most advantageous pressure for the desired-breakdown characteristics may be used.`

Although we do-not wish to limit ourselves tothe size of the bore of the intermediate tubular portion I2,l yetV we may -desire todecrease itfor makeit soy small that the discharge therethrough is saturated, that is, lls the entire cross-sectionv of the. .bore andi cannot be` further increased at thevpressurezused lby increasing the .size of the condenserf- Use at saturationcurren-ts notpnlymeans that the spectral characteristics of the energy consumption; is

and. aminorproportion of xenon, K

flashes are uniform, but that blackening is avoided.

We claim:

1. The method of making a discharge device comprising forming end chamber portions as graded seals, forming a pair of solid cylindrical metal electrodes, chamfering an end of each electrode for fitting in an end cup, fitting the chamfered end of each electrode into a cup of Kovar and spot welding it thereto, placing rings of brazing wire over each electrode, heating each electrode and associated cup in humid hydrogen at a temperature of about 1010 C. for about 20 minutes to braze each electrode toits cup, glassing the free edge of the cup of each electrode assembly, holding one of said graded seals with a protective ring of asbestos ribbon around its end in a lathe head chuck and a quartz intermediate portion tube with one end plugged with asbestos in the tail chuck of said lathe, sealing the adjacent ends of the parts, using a special flux glass on the quartz tube, disengaging the tail chuck and removing the asbestos plug from the quartz tube, plugging a second graded seal and holding it with a protective ring of asbestos ribbon in the tail chuck, making a second seal between it and the other end of said quartz tube, placing an electrode assembly in the tail chuck and sealing it to a graded seal, care being taken to avoid oxidation of the electrode, removing the assembly, turning it around and holding it in the head chuck, placing the other electrode assembly in the tail chuck, and sealing it to the other graded seal.

2. A discharge lamp comprising an intermediate fused quartz tubular portion, thick-walled to insure long life metal cup terminals one at each end thereof, graded seal glass portions forming end chambers with said metal cup terminals and hermetically sealing the respective ends of said low thermal expansion quartz portion to the higher thermal expansion metal terminals to complete the envelope of said lamp, a solid or non-tubular cylindrical refractory metal electrode, nearly as large in diameter as the bore of the tubular portion, extending inwardly from each metal terminal, disposed in the adjacent chamber, presenting to one another dat faces relatively large in area, and aligned axially with said envelope, each metal terminal having an inwardly opening socket, in which the outer end portion of its electrode is received and brazed, and a ange portion surrounding and spaced from its electrode, the free edge portion of said flange being hermetically sealed to the adjacent edge portion of said graded seal portion, and a filling of rare gas in said envelope.

3. A gas-filled discharge lamp comprising a thick-walled quartz tube about 2" long and l/5 inside diameter, a graded seal glass chamber of larger diameter hermetcally sealed to each end of and communicating with said tube, and solid refractory metal electrodes, nearly as large in diameter as the bore of said tube, presenting to one another fiat faces relatively large in area, disposed axially of said tube, one in each chamber.

4. A discharge lamp comprising an envelope, said envelope having an intermediate fused quartz tubular portion, thick-walled to insure long life, and metal cup terminals at each end thereof, said metal cup terminals closing the envelope and being hermetically sealed to the respective ends of said tube by graded seal portions forming end chambers and completing the envelope, a solid or non-tubular cylindrical refractory metal electrode, nearly as large in diameter as the bore of said tubular portion, extending inwardly from each metal terminal, disposed in the adjacent chamber, and aligned axially with said envelope, and a rare gas filling in said envelope.

5. A gas-filled discharge lamp comprising an outer tube of translucent refractory material selected from the group consisting of fused quartz, fused magnesia, and fused alumina, a glass chamber hermetically sealed to each end thereof, metal cup terminals at the outer ends of said glass chambers, and a solid or non-tubular metal electrode, nearly as large in diameter as the bore of said tube, in each chamber, presenting a flat surface to the other electrode with its outer end secured to the inner surface of the corresponding terminal, and disposed axially of said tube.

6. A discharge lamp comprising an intermediate tube of translucent refractory material selected from the group consisting of fused quartz, fused magnesia and fused alumina, about 2" long, 1/5 inside diameter and 3 mm. wall thickness, metal cup terminals one at each end of said lamp, graded seal glass portions, of a diameter larger than said refractory portions. forming end chambers with said metal cup terminals and hermetically sealing the respective ends of said refractory portions thereto to complete the envelope of said lamp, a solid or nontubular cylindrical tungsten electrode about 1/8 in diameter and 1%" long extending inwardly from each metal terminal, disposed in the adjacent chamber, presenting a flat surface to the other electrode and aligned axially with said envelope, each metal terminal having an inwardly opening socket in which the outer end portion of its electrode is received and connected, and a flange portion surrounding and spaced from its electrode, the free edge portion of said flange being embedded in, and hermetically sealed to, the outer edge portion of the adjacent glass end chamber, and a lling of noble gas comprising a major proportion of krypton at a pressure of about 325 millimeters in said envelope.

7. The method of making a discharge device comprising forming end chamber portions as graded seals, forming a pair of solid cylindrical refractory metal electrodes, tting an end of each electrode into a metal cup and electrically connecting it thereto to make the electrode assemblies, glassing the free edge of the cup of each electrode assembly, holding one of said graded seals with a protective ring around its end in a lathe head chuck and a quartz intermediate portion tube with one end plugged in the tail chuck of said lathe, sealing the adjacent ends of the parts, disengaging the tail chuck and unplugging the quartz tube, plugging a second end chamber portion and holding it with a protective ring in the tail chuck, making a second seal between it and the other end of said quartz tube, placing an electrode assembly in the tail chuck and sealing it to a graded seal, removing the assembly, turning it around and holding it in the head chuck, placing the other electrode assembly in the tail chuck, and sealing it to the other graded seal.

GEORGE A. FREEMAN. CARL G. ANDERSON, JR.

(References on following page) Number Name Date Meyer Sept. 20, 1932 Howe Oct. '11. 1932 Davies Nov. 21, 1933 Wiegand Aug. 28, 1934 Zecher Oct. 6, 1936 Gooskens May 3, 1938 10 Cox Dec. 27, 1938 Meyer Dec. 5, '1939 Number 10 Name Date Zecher Sept. 3, 1940 Suits May 13, 1941 Rentschler Sept. 2, 1941 Aicher Dec. 23, 1941 Beese Sept. 15, 1942 Grier Feb. 15, 1944 Marden Jan. 16, 1945 Blackburn Sept. 25, 1945 Germeshausen Apr. 30, 1946 Herzog Dec. 23, 1947

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