US2404057A - End-cap electrode for discharge lamps - Google Patents

Description

July W, 1946. D- s GUSTIN ETAL END-CAP ELECTRODE FOR DISCHARGE LAMP Filed March 24, 1943 INVENTORS .D. a GUJr/A/ fl. L. h EEMIq/V BY mu m ATTORNEY Patented July 16, 1946 END-CAP ELECTRODE FOR DISCHARGE LAMPS Daniel S. Gustin, Bloomfield, and Alva L. Herman, East Orange, N. J., assignors to Westinghouse Electric Corporation, East Pittsburgh, -Pa., a corporation of Pennsylvania 7 Application March 24, 1943, Serial No. 480,304

4 Claims.

This invention relates to discharge lamps and particularly to such lamps for the generation of ultra-violet radiations and wherein the ultraviolet is transmitted directly for use exteriorly of the envelope or utilized to excite a fluorescent coating and convert the invisible ultra-violet into visible radiations.

It is recognized that the ultra-violet output of lamps of this type is largely dependent on the area of the envelope through which the ultraviolet is transmitted on the coated area when the ultra-violet is converted into visible light. Heretofore, the electrodes have extended into the glass envelope and since the ensuing discharge is between the electrodes, this has resulted in an appreciable area at each end of the lamp from which no ultra-violet or converted visible radiations emanate, thus decreasing the efficiency of output for a given length of envelope.

It is accordingly an object of the present invention to provide a discharge lamp for the generation of ultra-violet radiations wherein the efiiciency thereof for a given length of envelope is increased.

Another object of the present invention is the provision of an ultra-violet lamp wherein the electrodes are so positioned as to in no way impair the emanation of radiations from substantially the entire envelope of the lamp.

Another object of the present invention is the provision of a lamp for generating ultra-violet radiations wherein the electrodes for the lamp constitute a seal for each end of the lamp as well as socket terminals, thus effectively positioning the electrodes at the absolute extremity of the envelope, thereby increasing the area of the latter through which radiations are transmitted.

Still further objects of the present invention will become obvious to those skilled in the art by reference to the accompanying drawing wherein:

Fig. 1 is a plan view partly in section of an ultra-violet lamp constructed in accordance with the present invention;

Fig. 2 is a sectional View taken on the line II-II of Fig. 1;

Fig. 3 is a sectional view taken on the line III-III of Fig. 1;

Fig. 4 is a fragmentary view of one form which a portion of the electrodes as shown in Fig. 1 may take, and

Fig. 5 is a fragmentary view similar to Fig. 4 and showing a modification which a portion of the electrodes may take.

Referring now to the drawing in detail, the

lamp 5 comprises a vitreous envelope 6 which is permeable to ultra-violet radiations if the latter are desired exteriorly of the envelope, or the envelope may be of ordinary glass provided with a coating 1 on the interior thereof which is excited by the invisible short-wave ultra-violet and fluoresces to produce visible light. An ionizable medium which may comprise an inert gas, such as neon, argon or a mixture thereof at about 15 to 20 millimeters pressure, together with a' small quantity of mercury II, is disposed interiorly of the envelope for the purpose of initiating and supporting a discharge in the customary manner.

At each end of the envelope 6 an electrode 8 is provided and since both are substantially identical, a detailed description of one should suflice. These electrodes are formed of a metal having a coefilcient of expansion simulating that, of the envelope such, for example, as the alloy commercially known as Kovar. As shown, such electrodes are sealed directly to virtually the extremity of the envelope 6 with just sufficient of its peripheral edge overlapping the electrode 8 to form an hermetic seal, thus effectively positioning the electrodes substantially beyond the extremity of the envelope so that radiations emanate throughout the entire length of the latter.

Such electrodes are of substantially cylindrical configuration with a curved closed end having a recess 9 therein, to enable the lamp 5 to be readily inserted in appropriate sockets. One of these electrodes 8 is provided with an opening ID in the end wall of the recess, which thus communicates with the interior of the envelope after the electrodes are sealed thereto. During fabrication of the lampfi, a glass exhaust tube L2 is sealed in the recess 9 through which the lamp is exhausted and filled with the ionizable medium. Upon completion the lamp 6 is sealed off by fusion of this exhaust tube until the latter forms a vitreous button l3'filling the recess 9.

In the form of the electrodes shown in Figs. 1 to 4, a short angularly disposed rod l4 of nickel or nickel-plated iron is welded at one end to the interior of the end wall of the electrode, and its other end is bent upon itself to form a clamp for holding a small piece of electron-emitting material such as thorium [5 substantially concentric with the electrode 8. During the seasoning process, thorium is sputtered from the small piece [5 onto the interior surface of the electrodes, which thus forms an electron-emitting surface [6 that is constantly replenished as need be during the life of the lamp. Moreover, since the thorium I5 is recessed well within the hollow electrode 8, substantially no sputtering of electron-emitting material onto the wall of the envelope -6 occurs during operation of the lamp, thus eliminating end blackening with decrease in radiation efiiciency as has heretofore occurred in such lamps.

In Fig. a slight modification, is shown which differs from that previously described merely in the provision of a metallic strip I! for the rod M of the preceding modification, with the free end of this strip being crimped around the thorium piece 18. This modification functions in the identical manner as that previously described, and in all other respects the complete electrode is identical to Figs. 1 to 4. 7

Upon the application of a suitable potential to the electrodes, a discharge occurs therebetween and since the ionizable medium is at a low pressure, such discharge substantially fills the interior of the envelope as distinguished from the pencil discharge attendant high pressure. Moreover, since the electrodes 6 are positioned at the very ends of the envelope, the discharge occurs throughout the entire length of the latter with no portion of the envelope being obstructed. This accordingly enables the radiations generated by the discharge to emanate from the entire area of the envelope, whether such radiations be ultraviolet or visible caused by excitation of a coating on the interior surface of the lamp 5.

'It thus becomes obvious to those skilled in the art thata discharge lamp is herein provided which has a greater efiiciency for a given length lamp than lamps of similar length heretofore known to the art. In other Words, the lamp of the present invention can be readily installed in existing fixtures having a fixed spacing between its sockets and for the same wattage input, a substantial increase in efficiency is obtained. Moreover, the electrodes themselves are employed as seals for the envelope and as the socket terminals, thus decreasing the mount of metal formerly employed and at the same. time such electrodes contribute to the construction of a more efiicient lamp.

Although several embodiments of the present invention have been shown and described, it is to be understood that still further embodiments thereof may be made without departing from the spirit and scope of the appended claims.

' We claim:

1. A discharge lamp comprising an envelope containing an ionizable medium, a pair of electrodes between which a, discharge occurs upon the application of a potential therebetween, said electrodes being hermetically sealed to the peripheral edge of the extremities of said envelope to dispose them entirely beyond the longitudinal limits of said envelope to substantially prevent sputtering of the electrode material onto the envelope wall and to increase the effective area of the envelope through which radiations are emitted for a given size envelope, and said electrodes forming a terminal readily engageable with a socket with at least one of said electrodes having a recess therein, and an exhaust stem hermetically sealed to the surface of said electrode both within and outside of said recess and fused thereto to substantially close said recess.

2. A discharge lamp comprising an envelope containing an ionizable medium, and a pair of electrodes provided with an electron emissive coating and between which a discharge occurs upon the application of a potential therebetween, each said electrode being disposed at an extremity of said envelope and forming an hermetic seal therewith and constituting terminals for engagement in a socket, a support projecting upwardly from a surface of said electrode, and an electron emissive material carried by said support entirely within the confines of said electrode and forming a reservoir for replenishment of the electron emissive coating on said electrodes during operation of said discharge lamp.

3. A discharge lamp comprising an envelope containing an ionizable medium, and a pair of electrodes provided with'an electron emissive coating and between which a discharge occurs upon the application of a potential therebetween, each said electrode being disposed at an extremity of said enevelope and forming an hermetic seal therewith and constituting terminals for engagement in a socket, a support projecting upwardly from a surface of said electrode, and a piece of thorium metal carried by said support within the confines of said electrode and disposed substantially concentric therewith and constituting a reservoir for replenishment of the electron emissive coatin on said electrodes during operation of said discharge lamp.

4. A discharge lamp comprising an envelope containing an ionizable medium, and a pair of electrodes provided with an electron emissive coating and between which a discharge occurs upon the application of a potential therebetween, and at least one of said electrodes including a support projectin from the wall of said elec trode and a piece of thorium metal carried by said support entirely within the confines of said electrode and substantially concentric therewith and constituting a reservoir for replenishment of the electron emissive coating on said electrodes during operation of said discharge lamp.

DANIEL S. GUSTIN. ALVA L. HERMAN.

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