GB645122A - Improvements in and relating to electric discharge devices - Google Patents

Abstract

645,122. Discharge lamps. BRITISH THOMSON-HOUSTON CO., Ltd. Sept. 7, 1945, No. 23132. Convention date, Sept. 11, 1944. [Class 39 (i)] A positive column discharge lamp comprises at least one electrode having front and rear members 8, 18, Fig. 2, of refractory sheet metal such as tantalum or tungsten, the front member 8 facing the discharge being disc-like, and the dished rear member 18 being electrically connected to the front member in such a way that heat conduction between the two members is restricted. In Fig. 2 the lead wire 9 is spotwelded to the centre of disc 8 which is also slightly dished, and the centrally apertured dished member 18 is carried by wire 19 from wire 9. The free end of lead 9 is spot-welded at 10 to the flattened side of the lead 6. In a modification, Fig. 3, the front member 8 is secured to the rear member 18 by a refractory wire 22 which is spot-welded in a diametrical position to front member 8 and has bent up ends spot-welded to the outside of the rear member 18. In this case the rear member 18 comprises a flat portion 21 and an annular portion 20. The electrode is carried by stout wire 9 from lead-in wire 6. The lamp may operate on A.C. or D.C. and may have one or two electrodes as shown in Figs. 2 or 3. In Fig. 1, the device has a borosilicate glass or quartz envelope 1, main electrodes 8, 8 and an auxiliary starting electrode 3. The filling is mercury and/or an inert rare gas such as argon, krypton, or xenon, and in operation the mercury vapour may be saturated or unsaturated. If argon is used it may have a pressure of 17 mm., and the mercury vapour may have a pressure of one or one and a half atmospheres, or more, so that the discharge is a constricted arc. The envelope 1 has reduced ends around the electrodes from which still further reduced necks 5 incorporating graded seals project. Member 18 has a smaller radius of curvature than member 8 ; they are both spherical segments. The lamp of Fig. 1 may be operated in any position from horizontal to vertical, but a modified form, Fig. 5 (not shown), must be operated in a vertical position. The lamp of Fig. 5 (not shown), is enclosed in an outer glass jacket filled with nitrogen at a pressure of half an atmosphere. In both embodiments the front disc 8 may be flat instead of dished, and is designed so as to obtain a uniform temperature distribution over its surface so as to avoid hot spots. The Specification as open to inspection under Sect 91 states that the front member 8 may be triangular, rectangular, or otherwise polygonal, need not be flat on either major face, and.may be used alone without the rear member 18. This subject-matter does not appear in the Specification as accepted.