GB614462A - Improvements in and relating to fluorescent electric discharge lamps - Google Patents

Abstract

614,462. Discharge lamps. BRITISH THOMSON-HOUSTON CO., Ltd. July 12, 1946, No. 20925. Convention date, April 21, 1945. Drawings to Specification. [Class 39 (i)] Blackening is prevented, in a discharge lamp having a coating of fluorescent material on the inner wall of the envelope and a filling of mercury vapour and argon, by adding nitrogen to the argon during the gas-filling process in the proportion of 0.6 to 1.1 per cent of nitrogen to 99.4 to 98.9 per cent of argon. During seasoning of the lamp in the factory the nitrogen cleans up and no nitrogen gas is present in the discharge space during ordinary operation after seasoning. The lamp is of the lowpressure, long-gap, positive column type with a diffuse discharge. 0.4 or 1.5 per cent of nitrogen is stated to lower the light output. The argon-nitrogen mixture is at a pressure of 2-6 mms., preferably 3.5 mms., and the mercury vapour is at 10 microns pressure. The lamp emits some ultra-violet light. The device may be hot or cold starting and may operate on D.C. or A.C. The cathodes may be coiled or coiled coil tungsten filaments coated or charged with alkaline earth oxides, e.g. a mixture of barium and strontium oxides, or as described in Specification 569,685. The Specification as open under Sect. 91 states that the percentage of nitrogen may be adjusted inversely as the tube diameter and inversely with the pressure, and refers broadly to rare gas as well as specifically to argon and to vaporizable and ionizable metal as well as specifically to mercury. This subject-matter does not appear in the Specification as accepted.