GB1095055A - Improvements in or relating to high pressure metal vapour electric discharge lamps - Google Patents

Abstract

1,095,055. Metal vapour lamps. PATENTTREUHAND - GESELLSCHAFT FUR ELEKTRISCHE GLUHLAMPEN m.b.H. June 6, 1966 [June 10, 1965], No. 25114/66. Heading H1D. High pressure metal vapour lamp operating at several atmospheres pressure comprising a sealed discharge tube mounted within an outer envelope and containing rare gas, mercury and one or more vaporizable halogen compounds, e.g. metal iodide, has a thermal switch between the two envelopes, the switch, with movable bimetal strip, having a resistive heating element, e.g. a coil, connected in series with one of the two lead-in wires and the contacts connected between the lead-in wires so as to short-circuit the tube when not in operation; the application of the supply voltage in this short-circuited mode causes the switch contacts to separate, producing a high voltage inductive pulse between the discharge electrodes, thereby initiating conduction. The heating element may also be the movable bimetal strip itself heated directly due to its inherent resistance, the strip being fixed at one end and its other end connected to the electrode by means of a flexible connector forming part of the lead-in wire. The lamp and switch thermal capacities can be such that on accidental extinction of the discharge, the contacts will remain open due to the residual heat stored until the tube has cooled to a temperature at which the gas pressure is sufficiently low for re-initiation by the switch mechanism.