GB440945A - Improvements in or relating to positive column electric discharge devices - Google Patents

Abstract

440,945. Discharge lamps. BRITISH THOMSON - HOUSTON CO., Ltd., Crown House, Aldwych, London. Sept. 20, 1935, No. 26113. Convention date, Sept. 20, 1934. [Class 39 (i)] In a positive column discharge device, a series of thermionic electrodes 11, 12a, 12 are arranged along the tube to facilitate the starting of the discharge ; the heating resistances of the electrodes are in series and this combined heating circuit is in parallel with the discharge gap. As shown, with equipotential electrodes, the oxide-coated emitting surfaces have connections 20 to the molybdenum connecting leads for the heating resistances, the leads being encased in alumina tubes 25. The four electrodes 11, 12a have sharp-edged, starting - anode pieces 24 of tungsten, which start a local discharge at the commencement of running. With the connections as shown, the potential drop will be greater between the top electrole 12 and the right-hand electrode 12a than between any other pair of adjacent electrodes, and an intermediate discharge will be first obtained across this gap to be followed by other intermediate discharges and finally by a discharge across the main gap between the electrodes 11 ; when this takes place the electrodes 12, 12a go out of action. In a modification, with three electrodes in a U-tube, the upper electrode is arranged across the tube, and the leads are taken outside the tube ; in another arrangement some of the electrodes may be directly heated. The filling may be of sodium with an addition of neon or argon whose partial pressure is between 1 to 7 mm. The lamp may be enclosed in an outer envelope.