GB599477A - Improvements in and relating to infra-red generators - Google Patents

Abstract

599,477. Discharge lamps. BRITISH THOMSON-HOUSTON CO., Ltd. Sept. 18, 1945, No. 24088. Convention date, Sept. 25, 1944. [Class 39 (i)] A generator of infra-red radiation comprises a cold cathode discharge tube 1 with a filling of mercury vapour and an inert gas, having an internal layer of phosphor 8, which when excited by the short-wave ultra-violet radiation of the discharge generates longer wave ultraviolet in the range 3400 to 4400 Š in turn, exciting an external layer of phosphor 9 to emit infra-red radiations. The inert gas may have a pressure within a range of a few millimeters to about 10 to 20 millimeters of mercury. The internal layer 8 consists of a cerium activated alkaline earth phosphate, e.g. calcium phosphate, or tungstate with a nitrocellulose binder removed by baking. The external layer is copper activated zinc-cadmium sulphide which contains, prior to firing at least 60 per cent of cadmium sulphide and preferably 70- 90 per cent. The electrodes 4, 5 are of nickel or iron and may be coated with barium, and the envelope is of glass permeable to long ultraviolet radiations, such as lime glass or a borosilicate glass, e.g. Corning glass No. 974 and may be suitably coloured to shield the eye from visible light. Alternatively, both layers of phosphor may be superimposed on one another on the interior of the wall or may be applied as a mixture. The discharge tube may be of the thermionic electrode type with a known circuit arrangement including a thermal switch as in Fig. 2 (not shown). Specification 517,526 is referred to.