GB410787A - Improvements in and relating to electric discharge lamps - Google Patents

Abstract

410,787. Discharge lamps. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London, and GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London.-(Assignees of Spanner, H. J. ; 117, Chausseestrasse, Berlin.) Nov. 21, 1932, No. 52875. Convention date, Nov. 21, 1931. [Class 39 (i).] In lamps of the "high-pressure" type having thermionic cathodes and a filling of permanent gas and metal vapour arising from a body of metal not forming the anode or cathode but strongly heated by the discharge, to thermionic electrodes are placed so near the end walls. of the tubular envelope that the heat from the discharge and radiation from the electrode keep the end walls at substantially the same temperature as the side walls and undesirable condensation of metal behind the electrodes is thus avoided. The vapour may be mercury at not less than 100 mm., cadmium, zinc, lead or bismuth, the envelope being of quartz or refractory glass. Cadmium-amalgum lamps are also referred to. The electrodes may comprise a nickel helix 4 filled with alkaline earth oxides and mounted on a short-circuiting clip 4<1> as described in Specification 397,162 and may be heated by the discharge itself or by an external souce of energy. The ends of the envelope closely surround the electrodes as shown and the lead 5 between the seal and the electrode is very short. To promote uniformity of temperature and avoid local overheating, the thickness of the walls can be varied, for example, the wall is thinned at 1 above the electrode 4. The accidentally thinned part at the sealing-off pip 2 is covered by an asbestos cap. The amount of the vaporized metal 3 is limited to that required to produce sufficient vapour pressure, extinction of the discharge by an increase in voltage and so in temperature and vapour pressure being thus avoided. In introducing the metal during manufacture of the lamp, one small portion is cooled whilst the rest of the lamp is kept warm. All the metal then condenses on the cool portion and its amount can be estimated and compared with a standard lamp. Several metals can be successively introduced in this manner. Specification 398,799 also is referred to.