GB493975A - Improvements relating to supply installations for electric discharge lamps - Google Patents

Abstract

493,975. Control systems for discharge lamps; flashlight photography. BRITISH THOMSON-HOUSTON CO., Ltd. Sept. 25, 1937, No. 26056. Convention date, Sept. 25, 1936. [Class 38 (iv)] [Also in Group XX] Switching control.-A gas discharge lamp 10, which may be of the metal vapour or low pressure gas discharge type, is arranged to provide momentarily increased brilliancy by short circuiting a stabilizing impedance 18 in series with it, through a timing relay 21 the time period of which is determined by a thermally variable resistance. When used for photographic purposes, the lamp 10 operates on closure of a switch 16 with sufficient intensity to permit focusing &c. of the camera. Closure of a double pole switch 25 causes short circuiting of the impedance 18 over contacts 23, 32 of the relay 21 and, at the same time, causes tripping of the camera shutter 40 over a relay 35. The coil of the relay 21 is connected to mains supply in shunt with a resistance having a positive temperature coefficient, such as a tungsten filament lamp 29, and in series with a resistance 27. On first switching in, the relay does not operate because of the low resistance of the lamp 29, the resistance of which rises rapidly and operates the relay to open the short circuit over contacts 23, 32 within a very short period, e.g. 1/20th second. The series impedance may be formed by a high reactance one-to-one ratio transformer which is shunted by the contacts 23, 32. The lamp may be flashed periodically for signalling purposes. Specification 462,500, [Group XL], is referred to.