GB675201A - Improvements in and relating to high pressure metal vapour lamps - Google Patents

Abstract

675,201. Metal-vapour lamps. BRITISH THOMSON-HOUSTON CO., Ltd. March 25, 1949 [March 27, 1948], No. 8198/49. Drawings to Specification. [Class 39 (i). The life of a high-pressure metal-vapour lamp of the type having a quartz discharge tube enclosed in an outer tubular vitreous envelope is prolonged by a suitable choice of glass for the outer envelope, and a suitable choice of dimensions for both envelopes, the latter chosen to give wall loadings within a specified range of watts per square centimetre. It is stated that deterioration is caused by the diffusion of hydrogen through the hot quartz into the discharge space, and that this unwanted hydrogen comes from the outer envelope. Accordingly, certain specified glasses are now used for the outer envelope to give better results than glasses previously used. The rate of diffusion of the hydrogen is further reduced by increasing the radiating area of both envelopes so as to lower the operating temperature. Exemplary dimensions are given for lamps of various ratings, and being designed to give a specific wall loading ranging from 1 to 1.5 watts per square centimetre for the outer vitreous envelope and from 8 to 13.2 watts per square centimetre for the inner quartz envelope. In the particular example described, the discharge atmosphere consists of mercury vapour at several atmospheres pressure in an unsaturated condition during operation, with argon at a few millimetres pressure. The space between the envelopes is filled with nitrogen at about half an atmosphere pressure. Specification 444,943, [Group XI], and U.S.A. Specifications 2,094,694, 2,135,690, 2,135,702, 2,177,685 and 2,247,176 are referred to.