GB451353A - Improvements in and relating to electric discharge devices - Google Patents

Abstract

451,353. Discharge lamps. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London. Jan. 2, 1935, No. 152. Convention date, Jan. 3, 1934. [Class 39 (i)] An enclosed arc lamp contains refractory metal electrodes coated or impregnated with thermionically active material, a heater for raising at least one electrode to operating temperature and a resistance heater as described in Specification 425,597 in the lead to one electrode in series with the arc and having a refractory insulating covering in heat-conductive relation to vaporizable metal. Each main electrode may comprise a refractory ball 16, Fig. 3, projecting towards the other electrode as shown in Fig. 2 and receiving the arc in normal operation, and a tube 13 or disc or cup coated with barium oxide to produce a glow discharge at starting and heated by a winding 21 about the tube 13 or about the central rod 15 supporting the ball 16. The windings 21 of the two main electrodes are connected in series across the arc by a conductor 36 connected to electrode points 431 facilitating starting ; after the arc starts, little current flows through the windings 21. The series resistance 32 in the lead to the lower main electrode is enclosed in a tube 30 of beryllium oxide, thoria, alumina or magnesia. The tube 30 is heated to luminescence and passes through a pool 35 of mercury to raise the vapour pressure in the arc and improve the yield of ultra-violet rays. In modified electrodes, the ball 16 may be omitted and an insulated heater surrounds a refractory metal, cylindrical roll impregnated with thermionic material. In a modified lamp (Figs. 7-10, not shown), an auxiliary starting electrode adjacent either main electrode or between the main electrodes has an internal heater connected through resistances to the two main electrodes. The Specification as open to inspection under Sect. 91 comprises also electrodes of nickelbarium alloy. This subject-matter does not appear in the Specification as accepted.