GB1211176A - High-pressure sodium vapor lamp - Google Patents

Abstract

1,211,176. Metal vapour lamps. GENERAL ELECTRIC CO. 13 Feb., 1968 [16 Feb., 1967], No. 7100/68. Heading H1D. Sodium cleanup in a high-pressure lamp comprising an alumina envelope 12 with a filling which includes mercury, an inert gas and sodium. said sodium being at a partial pressure of 10 to 1000 torr. in operation, is prevented by providing in oxygen-communication with said envelope a reactive metal substance, said metal having over a given temperature range a free energy of reaction in the formation of its oxide per mole of oxygen more negative than the free energy of formation of sodium aluminate per mole of oxygen within said envelope, said substance being so located within said lamp as to achieve during operation a temperature within said range. The metal substance may be the pure metal or a compound or alloy thereof. A list of 26 suitable metals is provided, those preferred being Y, Ce and Lu in that order. The sodium is preferably provided by a sodiummercury amalgam 26 and the inert starting gas may be xenon. The reactive metal may be provided in a dummy niobium exhaust tube 20, niobium being permeable to oxygen over the said temperature range. Alternative locations are as an internal or external coating on a niobium end cap 18, a coating 43 on a metal tab 44, or an addition 42 to the amalgam 26. The envelope 12 is supported by a frame 22 in an outer evacuated vitreous envelope 2 containing getters G, G<SP>1</SP> of barium powder which is at a temperature below said range.