GB431382A - Improvements relating to electric discharge lamps - Google Patents

Abstract

431,382. Discharge lamps. SIEMENS ELECTRIC LAMPS & SUPPLIES, Ltd., Caxton House, Tothill Street, London, and ALDINGTON, J. N., c/o Siemens Electric Lamps & Supplies, Ltd., Dock Road, Preston. Dec. 6, 1933, No. 34333. [Class 39 (i)] Hot-cathode, high-pressure, mercury-vapour lamps with the electrodes close to the ends of the elongated container to avoid condensation of the filling at these ends have a filling of mercury and additional metals adding red rays, the filling being introduced in unvaporized form and being of such composition, and the lamp being operated at such a watts dissipation as compared with the internal capacity of the container, that the deficiency of red rays in the mercury spectrum is compensated, at least 2 per cent of the light passing through a filter which passes only light above 5800 Angstrom units. Cadmium, zinc and bismuth are referred to and fillings consisting of an amalgam of 2, 3 or 5 parts of mercury with 1 part of cadmium and 1 part of zinc are specified, either of the metals cadmium and zinc being replaceable by the other. The watts dissipation per c.c. of the container is of the order of at least 3.5 and the voltage drop in the discharge reaches À5 volts per mm. and is not less than 50 per cent of the mains voltage. The efficiency decreases with increasing proportions of the additional metals and when the efficiency drops to 60 per cent of that of the lamp filled only with mercury, the increase in blue light from the additional metals renders the increase in red light of little value. Each main electrode may comprise a barium silicate core in a tungsten spiral transverse to the axis of the tube and may be associated with an auxiliary electrode comprising a tungsten spiral of large thermal capacity. The auxiliary electrodes are connected together through a high resistance as described in Specification 410,558. The container contains neon at 5-10 mm. pressure together with argon at 20-100 microns and the sealing pip of the evacuating tube is made small and located slightly in front of an electrode to keep it hot and so reduce condensation of metal in the pip. The container is enclosed in an outer exhausted envelope. Details of the design of the lamp are specified. The Provisional Specification describes also lamps in which the filling contains 1 part of mercury to 4 of cadmium to 1 of zinc and in which the mercury, but not the other metals, is all vaporized in operation so that the colour of the light can be adjusted by varying the watts consumed.