Patent GB-462356-A (GB)
Title: Improvements in and relating to electric discharge lamps
IPC: H01J61/34
Filed: 1935-08-30
Abstract: 462,356. Discharge lamps. BRITISH THOMSON-HOUSTON CO., Ltd. Aug. 30, 1935, No. 24309. Convention date, Aug. 30, 1934. [Class 39 (i)] In a metal-vapour, low-pressure discharge lamp the ballast resistance 22 is encased in an insulating tube 24 which incandesces to give red light for compensating the light deficiencies of the filling and to heat up evenly the walls of the envelope 10 to maintain the metal filling vaporized; this may be sodium at 1 or 2 microns and neon or argon at 1 to 7 mm. with a small amount of mercury, which filling with the incandescent tube gives approximately a white light ; the heaters for the cathodes are in parallel with the discharge gap. The electrodes are coated nickel tubes 34 drawn on beryllia insulators formed on the ends of the tube 24, the heater wires 30 being encased in these insulators. The tube is supported in a hole in a shield 42 placed with small clearance in the neck 13 of the envelope, this shield retaining the metal filling in the discharge space. As shown in Fig. 1, the heater wire extends in the tube only between the two electrodes and at its lower end is connected with an S-bend to the lead-in 15 ; at its upper end the heater 22 is connected to a wire 25, which is sealed to the top of the envelope. The wire 25 may also be cemented to the tube 24, but the arrangements permit extension of the resistance heater 22 during the mounting of the electrodes in the envelope. In the upper electrode, the electrode heater wire 30 is connected by a wire 31-lashed to the tube by molybdenum wire 36-to the wire 25 bv a flexible lead 37 which is also the connection to the nickel electrode tube 34. The lower end of the upper heater is connected to the lower heater by a lead 32 wound round the tube, the other end of the lower heater being connected to the lead-in 16 ; a lead 41 connects the lower electrode to this lead-in. In a modification, the wires 22 extend right through the tube 24. In a nickel tube 48-mounted on the lead-in 16-is carried a glass capsule containing the sodium filling, the capsule being ruptured by heating the tube inductively ; the tube holds the broken fragments. In a modification, two heater wires 22 acting as ballast resistance are arranged in parallel in separate tubes 24, Fig. 4, and are in series with the heaters 30a, Fig. 6, for the electrodes 20a. The tubes are supported in the shield 42a which carries the lead-in 16 on which is supported the lower electrode ; a lead 32a stayed at its middle by a wire 50 from the tubes 24 connects the lower and upper electrodes, the other end of the latter being connected to the wire 25a fixed in the envelope. This wire carries the cross-piece 25b which forms the electrical connection for the upper ends of the ballast resistances and also supports the tubes 24. In a further modification, three ballast resistances are arranged uniformly about central discharge electrodes ; two are connected together and then through the discharge gap to the third, all being in series. The containing tubes are spaced by a spider supported from the top of the tube. The discharge tube may be enclosed in an outer envelope and this and the inner envelope may be frosted. British Specification 425,597 and U.S.A. Specification 1,956,598 are referred to.