US2972698A - High-intensity light source - Google Patents

Description

Feb. 21, L. DANA ETAL HIGH-INTENSITY LIGHT SOURCE Filed Sept. 8, 1958 2 Sheets-Sheet 1 POWER SOURCE I h LINE OF ARC COLUrlNj!!l l SIGHT 46 /ELECTRODE 224 DC. Q y 2 POWER SOURCE GAS Brightness VS. Posirion in Arc Column INVENTORS LEO I. DANA Bra Q? a I Disfance From Nozzle or C8thode-inches A T TORNE V HAROLD S. MORTON,JR.

Feb. 21, 1961 l. DANA El'AL HIGH-INTENSITY LIGHT SOURCE 2 Sheets-Sheet 2 Filed Sept. 8. 1958 ELECTRODE DC POWER SOURCE WATER ARC cowmw-J 415 416 ums OF SIGHT GAS WATER FILM ELECTRODE POWER SOURCE \WATER SPRAY CONE WATER COOLED COPPER ANODE INVENTORS LEO I. DANA HAROLD S. MORTON,JR.

A TTO/PNE even replace, the carbon are for some uses.

HIGH-INTENSITY LIGHT SOURCE Lee I. Dana, Larchmont, N.Y., and Harold S. Morton,

Jr., Gaithersburg, Md., assignors to Union Carbide Corporation, a corporation of New York Filed Sept. 8, 1958, Ser. No. 759,765

9 Claims. (Cl. 313-231) This invention relates to high-intensity light sources and, more particularly, to high-pressure collimated electric arcs for such purpose.

According to the invention a concentrated high-intensity light source is obtained by passing a desired gas through the constricted arc of an arc torch of the type disclosed by Gage Patent No. 2,806,124.

'of the constricted arc and the brighter, extended light provide unexpected advantages over the prior art electric are light sources and, particularly, over prior light sources using xenon.

High-intensity light sources find important commercial applicaitons, particularly in motion picture projection work. In this application it is not sufiicient to have merely a source of high total light output. The opticsof the projection system make it desirable for this light to come from a concentrated, relatively even, illumination source.

The principal high-intensity light source now in use is the carbon arc. It is known in the art that arcs in xenon gas produce an extremely brilliant white light.

. Work has therefore been done in the field of developing a xenon are light source which might supplement, and Attempts were made in the known prior art xenon lights to increase the arc stability and to increase the area of high uniform brightness along the arc length by surrounding the arc with a narrow quartz tube, thus tending to wallstabilize the arc. However, the arc current was limited by the poor heat conductivity of the wall-stabilizing quartz envelope. As a consequence, the quartz envelope of the prior art high-intensity xenon lights was moved farther, from the arc column in order to increase the area for dissipating heat from this envelope. The collimation due to the tube was lost, and the arc was less elfectively stabilized. The resulting nonuniform cross sectional area of the arc column produced an extremely nonuniform brightness along the arc length, and the heat 1 dissipation through the quartz envelope was still the power-lirniting factor in this type of arc lamp.

The transferred arc torch produces an extremely stable, high intensity arc column which has relatively uniform brightness along its length. This is apparently due to the wall-stabilized, constricted arc produced within this torch, wherein the gas flowing through the torch nozzle collinearly with the arc tend to maintain the constricted fna'tu're of the'arc' column'over some distance from the end 'of the'nozzle'.

Any of the arc-supporting inert gases can be used with the torch, but the most useful gases with respect 2,972,698 Patented Feb. 21, 1961 electrode 10 was positioned coaxially within a /32-i116h diameter water-cooled copper nozzle 12. The electrode tip was set back ii -inch from the nozzle outlet. Argon gas at 20 c.f.h. was passed down around the electrode and out of the nozzle. An are 14 was then struck from the electrode 10 to a water-cooled copper anode 16 and maintained at about 40 volts (D.C.) and amperes. The are brightness under these conditions was measured to be about 4380 candles/cm. by focusing the light from that portion of the are just below the nozzle on a photometer. The current. was then varied from 50 amperes to 200 amperes, and the average brightness of the are just below the nozzle varied from 1710 to 6550 cd./cm. over this range of current.

This procedure was repeated with xenon gaspassing at a rate of 15 c.f.h. through the transferred arc torch. The brightness of the portion of the are just below the nozzle increased from 17,800 to 30,400 cd./crn. as the current was increased from 100 to 200 amperes.

As shown in Figure 2, an arc torch 23 comprising a -inch diameter tungsten electrode 22 positioned coaxially within a /s-inch diameter water-cooled copper nozzle 24 and set back Az-inch from the nozzle outletwas placed inside a pressure vessel 26 having a quartz window 28. The vessel was filled with xenon. An are 30 of 100 amperes and 21 to 38 volts (DCSP) was struck from the electrode to a water-cooled copper anode 32. The arc brightness was measured by focusing a portion of the arc image through the quartz window onto a photometer. The xenon pressure in the vessel was then gradually increased in measured increments from atmospheric up to 360 p.s.i.g. The peak arc brightness -in argon 34 and an argon-shielded transferred constricted are 36, under similar operating conditions.

The above information was obtained by viewing the are from the side in the conventional manner employed with are light sources. Occasionally an extremely bright point of light is required, for example, as the source of illumination for microscopy or Schlieren photography. For this application the arc can be viewed axially or end-on. This is accomplished with the transferred arc torch by employing an anode having a hole in the center and by viewing the are through this hole.

The following example gives data obtained for argon and xenon gases in an end-on-viewed transferred arc torch.

As shown in Figure 4, an arc torch was employed which consisted of a /Q, -inch diameter tungsten electrode 42 positioned coaxially within a Aa-inch diameter watercooled copper nozzle 44. The electrode tip was set back -inch from the nozzle outlet. A disc-shaped anode 46 having a y -inch diameter hole 48 was positioned As-inch below the torch nozzle. Argon was passed ata rate of 20 c.f.h. downthrough the torch while an 1955, now U.S. Patent No.-2,8 58,411,"issued October 28, 1958) can also be employed as a 'point-of-light'source. In this case no externalano'de is required, and the arc is viewed end-on through the torch 'nozzle.

' The transferred and 'noiitrans'ferred arc torches, when used as point-of-light sources, have advantages in that the constricted arc'enabl'es one to obtain light sources which are more stable and brighter than point-of-light sources of the prior art.

It is often desirable to use a transparent non-conducting nozzle to constrict an arc column over a major portion of its length. This would enable a larger fraction of the radiation from the arc to be utilized and would eliminate the double-arcing problem often encountered with conducting nozzles at high degrees of constriction.

Figure 5 shows an inert gas constricted arc50 established within a water vortex channel. A quartz water guide tube 52 was employed. This particular apparatus modification is described in more detail in copending application Serial No. 689,370, filed October 10, 1957,

now Patent No. 2,906,858.

Side-on brightness determinations were made of this water-wall constricted are using argon and viewing the column through the quartz and water walls. The are column was constricted a small amount and had a brightness of 8,000 cd./cm. at 250 amperes.

What is claimed is:

1. A source of light comprising a pair or axially aligned electrodes spaced from each other to provide an arc gap, one of said electrodes consisting of a stick composed of tungsten, the other one of said electrodes consisting of a hollow member composed of copper, means for circulating cooling liquid through said hollow electrode to prevent it from overheating, means for energizing a high pressure electric are between said electrodes including a source of direct current power connected to said electrodes so that said stick electrode is the cathode and said hollow electrode is the anode, means for feeding an annular stream of inert gas selected from the class consisting of argon, krypton and xenon along the end portion of said cathode adjacent such arc, and a coo-led nozzle for such arc provided with an are constricting outlet through which the arc and inert gas are discharged to produce an exposed column of a partially wall-stabilized inert gas electric arc, which is stable and characterized by relatively uniform brightness along the exposed arc length.

2. Method of producing light which comprises producing a Wall-stabilized arc, passing an inert gas stream through such wall-stabilized electric are so thatsuch stream becomes part of such are in the form of a column, the exposure of which provides a source of light, said exposed arc column being characterized by stability and stiffness by virtue of the fact that a portion of the arc column is wall-stabilized and such gas stream tends to restrict and stabilize the arc, the resulting exposed arc column also having relatively uniform brightness along its length.

active application'Serial No. 539,794, filed O'c'tob'ef 1 3. A lamp comprising apparatus for producing concentrated high-intensity source of light consisting of an arc column comprising ionized xenon gas resulting from an electric are which is wall-stabilized in and discharged from a constricting orifice, which apparatus includes the combination of a pair of axiallyaligned electrodes spaced from each other to provide an arc gap, one of said electrodes consisting of a'stick,'the other one of said electrodes consisting of a hollow member, means for circulating cooling liquid through said hollow electrode stabilized constricted arc torch, and means for discharging from such torch an exposed arc-gas efiiuent column, characterized by the use in such column of inert gas selected from the class consisting of argon, krypton, and

xenon.

5. A method of producing light which comprises striking a high-pressure electric are between a cathode and an anode inside a pressure vessel'h-aving a transparent viewing port; wall-stabilizing and collimating said arc by passing it through a cooled nonconsumable nozzle; passing an inert gas stream at a pressure above atmospheric along said cathode and through said arc-stabilizing nozzle so that said gas stream becomes collinear with said arc; said collimated are light source being extremely stable and having relatively even brightness along its arc length.

6. A method according to claim 5, wherein said gas is maintained by said inert gas stream at 15 to 50 atmospheres pressure within said pressure vessel.

7. A method of producing light which comprises striking a high-pressure electric are between a rod cathode and an anode inside a pressure vessel having a transparent viewing port; wall-stabilizing and collimating said arc by passing it through a cooled nonconsumable nozzle; passing an inert gas stream selected from the class consisting of argon, krypton, and xenon at a pressure above atmospheric along said rod cathode and'through said arc-stabilizing nozzle so that said gas stream becomes collinear with said arc,'said collimated are light source being extremely stable and having relatively even brightness along its arc length.

' 8. A method according to claim 7, wherein said gas is maintained by said inert gas stream at 15 to 50 atmospheres pressure Within said pressure vessel.

9. Method of producing high intensity light which comprises striking a direct current high pressure are between spaced axially aligned electrodes, constricting such arc laterally by'a nozzle having an orifice axially aligned with such electrodes, through which orifice such arc'is maintained by a continuous flow of inert gas, while co'ntinuously cooling the inner wall of such orifice by flowing cooling water through a water passage in the wall 'ReferencesCited in the file of this patent UNITED STATES PATENTS 2,540,256 Gretener Feb. 6, 1951 2,663,792 I Gretener Dec. 22, 1953 2,819,423 Clark Jan. 7, 1958

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