US2116702A - Electric gaseous discharge lamp - Google Patents

Description

May 10, 1938. J. KERN ET AL ELECTRIC GASEOUS DISCHARGE LAMP Filed Nov. 4, 1937 4 AMA. A TORNEY INVENTORS J 0 se? Ker-n H er-mann Kr eFFE Fig. 2

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Patented May 10, 1938 2,116,702 ELECTRIC, GASEOUS DISCHARGE Josef Kern, Berlin, and-Hermann Krcflt, Berlin- Friedrichshagen, jGermany, assignors to Geheral Electric Company, a corporation of New York Application November 4, 1937, Serial No. 172,826 f In Germany November 24, 1936 3 Claims. (or 176-124) The present invention relates to electric gaseous discharge lamps, and especially to lampsof this type which are adapted to use for projectionpurposes.

A particular object of the invention is to pro vide a light source of extremely high brilliancy and of considerable area, adapted for use in an optical projection system. A further object of the invention is to provide a light source of high luminous efllciency having a long useful life. Still other objects and advantagesof the invention will appear from the following detailed specification or from an inspection of the accompanying drawing.

The invention consists in the new and novel, combination of elements hereinafter set forth and claimed. o

Electric gaseous discharge lamps, particularly of the mercury arc type recently, introduced on the market, wherein a pressure exceeding ten atmospheres is attained during operation, have many advantages, among them being high inminous efliciency, Due to the extremely high vapor pressure the are within these lamps isconstricted into the form of a thread of extremely high intrinsic brilliancy, of the order of 20,000 candles per square centimeter, and more. Similar constricted arcs are also attained in lamps wherein fixed gases are presentat high pressure.

For many purposes, especially for purposes of projection, however, not only the intrinsic brilliancy is important but also the absolute sizeand shape of the light-radiating area; that is, the total light flux. In most cases a lightsource having' a shape as circular as possible is desired, Attempts of various kinds to spread-out the light-radiating high pressure light are, which with a current strength of several amperes still is thread-shaped, for instance byraising the discharge current strength with a simultaneous reduction of the vapor pressure or by the use of magnetic fields which draw the arc apart, heretofore have not had the desired led to great technical dimcultiesj We have now discovered, howeventhat an enlarged and substantially circular luminous area is achieved without raising the are burning voltage or the arc current strength, while retaining and in most cases even essentially increasing the luminous densty of the high pressure discharge are, if instead of a single high pressure discharge are, several independent high pressure discharge arcs are arranged beside each other in a common more or less spherical discharge vessel. Here the new and unexpected phenomenon was found, that success or have u when such high pressure discharge arcs are arranged beside each other in a common discharge space, they unite into a unitary luminous area,

as a result of the interaction of their own magnetic fields and by their. endeavor to adopt a common discharge path. As a result the entire field lying between the electrodes turns into a unitary uniformly luminous area of extremely high luminous density, especially with a very small electrode-separation.

According to ourinvention an electric metal vapor discharge lamp of the type which is adapted for operation with a vapor pressure of the order of II atmospheres has three or more thermionic electrodes arranged around the lightcenter of a spherical or short tubular discharge vessel. 0 These electrodes are fed with current in such a manner that two or more discharge arcs, which, are formed between them either simultaneously or with a phase displacement, produce a luminous area which includes more than 50% of the field bordered by the electrodes. I

with such high pressure discharge lamps constructed according to the invention a large number offavorable construction forms are possible, which differ from one another principally in the in the discharge vessel, in thekinds of current and the phase relations used in feeding the electrodes, as well as in the method of connecting the electrodes with the current sources.

For feeding the discharge arcs, electrically separated current sources are preferably used, such as separate transformers or a single transformer with several separate secondary windings. With suitable wiring and electrode arrangement it is also possible in many cases to produce the number of electrodes used and their arrangement different discharge arcs by means of a single transformer having several secondary windings that are electrically connected with each other in a manner, described hereinafter. Under certain conditions, even a single current source sumces, if a suitably proportioned resistance is connected in series with each pair of electrodes. As a mile, a phase-displaced feeding of theindividual current circuits is expedient, while in some few cases it is necessary. For the achievement of such a phase-displacement, phase-displaced current sources are used, or various kinds of impedances, such as choke coils, condensers or purely ohmic resistances or also combinations of these, can also be included in the current circuits. For anexact setting of the phase-displacement which is most favorable at the time, a regulatable former can also be used. Likewise the individual current circuits may be operated, where desired, with difierent kinds of electric currents and also voltages as well as frequencies. Thus one discharge are is in some cases operated with direct current and another one with alternating current. In one form of a high pressure discharge lamp constructed according to the invention a substantially spherical discharge vessel has four thermionic electrodes arranged in a square, the mutual separation of which amounts to at most 20 mm., preferably only 3-6 mm. When a high pressure discharge lamp constructed in this mane ner has diagonally opposite pairs of electrodes connected with two electrically separated alternating current sources so that the currents from these sources are phase-displaced by about 90, then, during operation the surprising phenomenon is produced, that not only do the expected two diagonally-running, alternately consecutive discharge arcs occur, but that, aside from these, unexpected discharge arcs are also formed between the adjacent electrodes fed from diflerent current sources, and furthermore, that these discharge arcs merge with each other in such a manner that almost the entire field bordered by the electrodes turns into a uniformly luminous I area of unusually high luminous density, thereby producing an ideal light source for projection pu p ses- In another favorable construction form having a short tubular discharge vessel, two opposing rows of two or more thermionic electrodes each, arranged in straight lines or in a circular are, are built-in in such a manner that the separation of the electrodes of one row is smaller than the separation of the two electrode rows. These electrodes are fed with current by means of suitable, well known circuits so that the electrode rows are bridged by several discharge arcs which are crowded closely together. In some cases these arcs are strung together zigzag fashion,.or even cross each other.

For the operation of the new high pressure vapor lamp with polyphase current, three thermionic electrodes are arranged triangularly, or four electrodesare-fixedin the form of a star, near the vessel midpoint. Or, where preferred, six electrodes arranged in the form of a hexagon can also be used. "These six electrodes are st/ connected with the three electrically separated secondary windings of a polyphase transformer that in each case two opposite'electrodes" are connected over a resistance with the endsof one secondary winding. In this case not only are there formed the expected three temporallyconsecutive, diagonally-running discharge arcs, but also a plurality of unexpected discharge arcs between the adjacent electrodes and also between the, electrodes displaced 120, which are fed by different secondary windings. Here all the discharge arcs flow into and merge with one another in such a manner that practically the entire field lying between the electrodes becomes a luminous area of a uniform luminous density.

Furthermore, with a high pressure vapor lamp containing several discharge arcs according to the invention, the thermionic electrode pairs can be so arranged behind each other or displaced sidewise with respect to the direction of light radiation so that the discharge arcs as seen in the direction of lightradiation complement each other into a unitary luminous area.

As is well known, these high pressure vapor lamps ordinarily contain an ignition facilitating gas filling of suitable pressure, for instance arson or neon at 20 mm. pressure, in addition to a metal base body which delivers the high pressure vapor atmosphere during operation. As a rule the amount of the metal base body is accurately measured in order to limit it to such a quantity that all the metal completely vaporizes in the operation of the discharge vessel, and preferably before the device reaches its equilibrium temperature, so that the produced metal vapor is superheated in considerable measure, in order that the arc voltage, which depends on the vapor density, remains unchanged during operation even with voltage and temperature fluctuations of the surroundings. The metal base body, instead of a single metal, can also consist, where desired, of a metal mixture, so that during operation a mixed light radiation results, which is composed of the spectra of two or more metal vapors.

The high pressure vapor lamp, as is well known, can furthermore have auxiliary electrodes, for instance, in order to be able to surely ignite and operate the lamp on very low voltages.

As a rule, the high pressure vapor lamps constructed according to the invention are provided in a well known manner with cooling arrangements, for instance compressed air cooling. In most cases, however, it will be expedient to-house the vessel surrounding the high pressure discharge arcs in a mantle-vessel, through which cooling water passes.

For the purpose of illustrating our invention we have shown several thereof in the accompanying drawing, inwhich Fig. 1 is an elevational view of a discharge lamp especially designed for use on a two phase system,

Fig. 2 is a similar view of a modification of the structure of Fig. 1 together with a single phase operating circuit therefor, and

Fig. 3 is an elevational view of a further modification of the structure of Fig; 1 which is especially designed for use in the three phase system which is schematically illustrated.

In this drawing, with special reference to Fig. 1, there is shown a high pressure metal vapor lamp having a spherical discharge vessel l consisting of'quartz or of a high-melting glass, which vessel ,/has four right-angularly placed, outwardly projecting fuse-in nipples 2, into which the current feed wires 3 are fused, diagonally opposite pairs of which are connected to the two electrically separated transformers 4, S/through the series chokes 6, I. The voltages supplied by these transformers are out of phase, preferably by 90. The discharge vessel l contains four dischargeheated thermionic electrodes I of the usual construction arranged in the form of a square. These electrodes are provided with strongly electron emitting substances, for instance with alkaline earth metal oxides, thorium oxide or mixtures of such oxides, for the purpose of reducing the electrode drops. The discharge vessel l further contains a gas filling which facilitates the ignition of the lamp, for instance a filling .01 neon or argon or a mixture of neon and argon or hellum with a pressure of 10-30 mm., as well as a mercury body 9 which vaporizes completely during operation. During operation of the lamp, the expected phase-displaced discharge arcs are formed between the adjacent electrodes, with the result that virtually the entire field lying between the electrodes becomes a luminous area of unusually high intrinsic brilliancy. In the middle part of the field, the discharge arcs flow into preferred embodiments amounts to only a few millimeters. The energy for this lamp is supplied by atransformer l6 having three secondary windings l1, ll, I! which are so connected with each other in the form of a cascade and so attached to the electrodes of the lamp that, in each half-wave of the alternating current, the two electrodes l2, ll of the lower row and also the two electrodes I 3, l of the upper row, each have the same polarity. During operation of the lamp the windings I1, I 8 and I9 lead to a discharge are from each of the electrodes l2 and H to each of the electrodes l3 and I5, respectively. These discharges cooperate with each other to substantially fill the area bounded by the electrodes with a light source of substantially uniform intensity. Instead of two electrode pairs, three or more electrode pairs can also be used and strung behind each other in which case five or more secondary windings are provided.

In Fig. 3 a high pressure vapor lamp for polyphase current operation is shown, the spherical discharge vessel of which contains six thermionic electrodes 20, which are arranged in the form of a hexagon around the midpoint of the discharge vessel I at a mutual separation of a few millimeters. For feeding the hot electrodes 20, a polyphase transformerZl is used, having the primary windings 22, 23, 24 delta connected. The three secondary windings 25, 26, 21 are electrically separated from each other and are connected with the electrodes 20 over thecurrent-limiting chokes 28, 29, 30 in such a manner that the two ends of each secondary winding are connected with two diagonally opposite electrodes 20. During operation of this lamp, a great number of phase displaced discharge arcs are formed, including diagonally-running discharge arcs between the opposing electrodes, as well as discharge arcs between adjacent electrodes following the sides of the hexagon, and finally discharge arcs between electrodes which are displaced by 120. All these discharge arcs together result in an outstandingly good and uniform luminosity of the field bordered by the electrodes.

While we have shown and described and have pointed out in the annexed claims certain novel features of the invention, it will be understood that various omissions, substitutions and changes in the forms and details of the device illustrated and in its use and operation may be made by those skilled in the art without departing from the broad spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States, is

1. In combination, an electric gaseous discharge device comprising a sealed envelopehaving three or more activated thermionic electrodes arranged therein with a relatively short gap therebetween, a gaseous atmosphere within said envelope adapted to support a high intensity constricted discharge between said electrodes,

and means to connect a plurality of sources of electrical energy to separate pairs of said electrodes to produce a plurality of constricted arc discharges between said electrodes with the path of at least two of said discharges intersecting, whereby the luminous area produced by said discharges is at least 50% of the area bounded by said electrodes.

2.In combination, a metal vapor arc lamp comprising a sealed envelope containing a gasee ous atmosphere and a vaporizable metal in a quantity suflicient to give an operating pressure of the order of 10 atmospheres, and having three or more activated thermionic electrodes arranged therein with a relatively short gap therebetween, and means to connect a plurality of sources of electrical energy to separate pairs of said electrodes to produce a plurality of constricted arc discharges between said electrodes with the path of at least two of said discharges intersecting whereby there is produced a rela tively large field of high luminosity of the order of 50% of the area bounded by said electrodes.

3. In combination, an electric gaseous discharge device comprising a sealed envelope having three or more activated thermionic electrodes arranged therein with a relatively short gap therebetween, a gaseous atmosphere within said envelope adapted to support a high intensity constricted discharge between said electrodes, and means to connect a plurality of phase-displaced sources of electrical energy to separate pairs of said electrodes to produce a plurality of constricted arc discharges between said electrodes with the path of at least two of said discharges intersecting, whereby the luminous area produced by said discharges is at least 50% of the area bounded by said electrodes.

JOSEFKERN.

HERMANN KREFF'I.

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