US2094695A - Vapor electric discharge device - Google Patents

Description

Oct; 5, 1937. A c. BOL' ET AL VAPOR ELECTRIC DISCHARGE DEVICE Filed April 10, 1936 Inventors: Cornelia Bol, Hendricus- J. Lemmens,

b Wwvu/ Their" Attorneg.

Patented Oct. 5, 1937 PATENT OFFICE VAPOR ELECTRIC DISCHARGE DEVICE Cornelis B01 and Hendrlcus J. Lemmens, Eindhoven, Netherlands, assignors to General Electric Company, a corporationof New York Application April 10, 1936, Serial No. 73,746

- In Germany 4 Claims.

The present invention relates to improvements in high pressure mercury vapor electric discharge lamps of the type described in copending application, Serial No. 46,952, filed October 26, 1935,

5 by Cornelis Bo], Willem Elenbaas and Hendricus J. Lemmens.

The aforementioned application" discloses and claims broadly a mercury vapor discharge lamp comprising a capillary quartz envelope having an internal diameter on the order of 7 millimeters and adapted to be operated at a very high speciflc loading as measured in watts input per unit of envelope length. It is pointed out, for example, that air-cooled tubes within the scope of the invention may employ a specific loading of from 25 to 100 watts per centimeter with a speciiic voltage drop of the order of from 75 to 300 volts per centimeter. Water-cooled tubes may consume from 150 to 1000 watts per centimeter with a specific voltage drop along the discharge path as high as from 100 to 1000 volts per centimeter.

As a result of these operating conditions and the particular conformation of the envelope,

mercury vapor pressures in excess of 10 atmospheres and running as high as at least 17 0 atmospheres may be realized in lamps of this type. Furthermore, very great luminous intensity is produced, a surface brightness as great as 30,000

International candles per square centimeter being easily reached.

While these lamps are well adapted for general indoor and outdoor illuminating purposes, they have been found especially advantageous for 3 projection lighting as, for example, in motion picture production in which an extremely concentrated and well-defined light source is desired. For this reason it is desirable to avoid insofar as possible any diffusion of the light generated by the high pressure discharge.

In the operation of lamps of this type in which the envelopes comprise straight quartz tubes of uniform internal diameter a tendency has been observed for etching of the quartz to occur in the central region of the discharge path. This is considered to be due to the very high temperatures developed in that particular region by the discharge, and the inadequate cooling of the same in comparison with the portions of the tube adjacent the lead-in conductors.

The present invention provides an improved construction in which the bore of the central portion of the envelope intermediate between the discharge electrodes is slightly enlarged to insure more satisfactory operation, The enlargement March 20, 1935 of the bore should not, however, be more than about 2 millimeters in excess of the remaining parts of the capillary, since an excessive enlargement tends to result in local condensation of the mercury and makes the maintenance of the desired high pressure diflicult.

By enlarging the central portion of the envelope in the manner specified, it has been found that etching of the glass in the central region may be considerably reduced, or even eliminated, so that no diffusion of the transmitted light occurs.

The single figure of the drawing illustrates schematically a water-cooled lamp embodying the improved construction of our invention. In the embodiment shown the discharge envelope comprises a capillary tube I which is cylindrical for the greater portion of its length. As described in the aforementioned B01, Elenbaas and Lemmens application, Serial No. 46,952, this tube has a bore the internal diameter of which is less than 7 millimeters and preferably from about 1 to about 5 millimeters. The walls are of a transparent material such as quartz which is adapted to withstand the high temperatures and pressures encountered during the lamps operation. Their thickness should be of the order of but preferably not greater than the internal tube diameter.

The tube is provided at each end with thermionic electrodes 2 which may comprise a tungsten core member having overwound thereon a finer tungsten filament, the whole being coated with an electron-emissive material such as barium oxide, or a mixture of the oxides of strontium and 1 barium. Tungsten lead-in wires 3 are introduced through the ends of the quartz tube by means of a graded seal comprising a substantially alkalifree boro-silicate glass as described in copending application, Serial No. 43,230, filed October 2,

1935, by Cornelis B01, Hendricus J. Lemmens, and Gottfried Jonas. Within the tube the portions of the electrodes adjacent the seals are surrounded by small bodies of 'mercury 4 which are strongly heated and thereby at least partially vaporized during operation of the lamp. A slight amount of a readily ionizable gas, such as argon or neon, is also enclosed in the envelope to assist in starting the discharge.

The parts of the lead-in wires which are outside of the envelope are encased in small insulating tubes 5. These are led through stoppers 6 of insulating material which close the ends of the glass cylinder I through which water or other suitable cooling fluid is passed.

As an example of particular dimensions which may be chosen for our improved construction,

. to about 2 millimeters.

cylindrical tube whose inside diameter amounts The corresponding wall thickness is about 2.5 millimeters and the distance between the thermionic electrodes 2 is about 20 millimeters, while the latter project about .25 millimeter out of the mercury globules 4. In accordance with the invention the central portion of the tube is slightly enlarged in diameter so that at the region designated by the numeral 8 the internal bore is about 3 millimeters.

Lamps of this construction may be operated from an alternating current source in series with an external impedance of such nature that the specific loading of the lamp reaches the high values specified in the foregoing. In consequence of the enlargement of the middle portion of the envelope in accordance with the present invention the lamp runs at essentially uniform temperature throughout its length in spite of the extreme pressures and are temperatures developed. For this reason and because the central portion of the discharge arc is prevented from playing directly on the tube walls etching of the glass and consequent diffusion of the light is substantially avoided.

The high pressure mercury lamps, comprising a quartz tube of small diameter, is the joint invention of the three inventors, Cornelis Bol, Willem Elenbaas, and Hendricus J. Lemmens. That invention is claimed in their application S. N. 46,952, filed October 26, 1935. The central enlargement of the lamp bore which is claimed in the present application is the joint invention of the two inventors, Cornelis B01 and Hendricus J. Lemmens. quently to the invention of the high pressure mercury lamp as claimed in the aforesaid application S. N. 46,952 and with full knowledge of that invention.

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

1. A high pressure discharge device adapted to be operated at a specific loading of from 25 to watts per centimeter and a specific voltage drop of from 75 to 300 volts per centimeter comprising a capillary quartz envelope of less than 7 millimeters internal diameter having electrodes sealed into the ends thereof and enclosing a suflicient quantity of mercury to produce under operating conditions a pressure of at least 10 atmospheres, said envelope having end-portions of substantially uniform internal diameter and a central inter- It was invented by them SUbSQ".

. 2,094,695 we have found the following to be suitable for a mediate portion of slightly enlarged internal diameter.

2. A vapor electric discharge lamp comprising an envelope having an inside bore of the order of 7 millimeters in diameter and a wall thickness of the order of the diameter of the bore, electrodes one at each end of said envelope, lead-in conductors for said electrodes hermetically sealed into said envelope, said envelope comprising a straight tube of a transparent heat-resisting material. such as quartz having at the central portion thereof and intermediate between said electrodes an enlargement .of the inner bore sulficient to produce substantially uniform temperature distribution along the tube length but not more than a few millimeters greater than the internal diameter of the remaining parts of the tube.

3. A mercury vapor electric discharge lamp comprising a, capillary discharge tube having an inside diameter of the order of from 1 to 5 millimeters and having a wall composed of high melting point light-transmitting material such as quartz and a solid electrode located in each endportion of the tube, lead-in conductors for said electrodes sealed into the end-portions of the tube, globules of mercury at each end of the tube and surrounding a portion of said electrodes adjacent said lead-in seals, said envelope comprising straight capillary portions extending from each of said electrodes toward the center of said tube, and a section intermediate between said straight portions having a bore sufilciently enlarged to obviate etching of the wall surface thereof during the normal operation of said lamp.

4. A high pressure mercury vapor lamp com- .prising a capillary discharge tube of a transparent heat-resisting material such as quartz, a pair of electrodes respectively disposed at each end of said tube, lead-in conductors for said electrodes, a quantity of mercury within said tube, and means for circulating a liquid cooling medium about the tube, said tube comprising endportions having a uniform bore of from 1 to 5 millimeters internal diameter and an intermediate central portion having'an internal diameter a few millimeters in excess of the internal diameter of said end-portions whereby said tube is maintained at substantially uniform temperature throughout its length even with a specific loading of from to 1000 watts per centimeter.

CORNELIS BOL. HENDRICUS J. LEMMENS.

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