GB505096A - Improvements in and relating to electric discharge lamps - Google Patents

Abstract

505,096. Metal-vapour lamps. BRITISH THOMSON-HOUSTON CO., Ltd., GILSON, C., BOURNE, H. K., and SCOTT, W. J. Nov. 3, 1937, No. 30.168. [Class 39 (i)] In high-pressure mercury-vapour lamps, for the purpose of causing the mercury to condense at the ends on switching off the envelope 4 is a uniformly bored tubular member of glass or quartz and the electrodes are formed of tungsten rod 5 ground to fit the bore of the tube. The exhaust tube is preferably placed opposite the shank of the electrode to avoid formation of the cooling area made by the sealing of pip in the central part of the envelope, and for the purpose of evacuation, a longitudinal groove 7 is provided in the electrode registering with the exhaust tube. A circumferential groove 10 is also provided to lock the electrode in place when the tube is melted down on it. The sealing of the tungsten electrodes may be done by winding a helix of molybdenum foil over all the portions of the electrode on which the hot quartz will be sunk, and a rod of quartz may be enclosed in the quartz ribbon to form a support therefor. The lip of the electrodes may be made conical as described in Specification 462,545 and for high current density lamps operating at 20 atmospheres may be activated by a thick or a monatomic coating of an alkali metal or salt, and may also have a portion roughened by growing a crystalline structure thereon in wet hydrogen. The quantity of mercury may be limited so as to be superheated at operating temperatures.