GB1498258A - High pressure mercury vapour discharge lamp - Google Patents

Abstract

1498258 Metal vapour lamps PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 7 May 1975 [9 May 1974] 19166/75 Heading H1D In a high pressure Hg lamp, with or without electrodes, the volatility of the alkali or alkali earth metal halide (Cl, Br, I) responsible for light emision is increased by introducing volatile Al halide (Cl, Br, I) forming a gaseous compound with the first halide. In two designs of conventional double-walled envelope 400 W HP lamp running with silica arc tube wall temperature of 700-800‹ C., containing Hg and inert gas (e.g. Ar), NaI is made volatile with AlCl 3 or NaBr by AlBr 3 , combined chlorides being efficient but tending to attack W electrodes, leading to wall blackening. The molar proportions of the two halides should be near 1 :1. Octer volatile-halide-forming metals may be partially substituted for Al; in general a highly volatile halide which forms a dimer in the vapour and a poorly volatile halide which also forms a dimer in the vapour are likely to combine to form a volatile letrodimer : volatile halides of Fe<SP>+++</SP>, Tl<SP>+</SP>, In<SP>+++</SP>, Sn<SP>++</SP> are suitable. With Na halide present, the increased volatility tends to shift the colour temperature, but this may be compensated by varying the composition of the volatile halides. Other alkali metal or alkali earth metal halides together with other poorly volatile halides (other than-F) such as those of Cd, Ga, Sc, Y or rare earths may also be substituted for Na halide.