METAL HALIDE DISCHARGE LAMP

1283152 Metal-halide lamps GENERAL ELECTRIC CO 10 April 1970 [19 May 1969] 17261/70 Heading HiD The filling of a metal-halide lamp contains an inert gas e.g. 25 torr of argon, SnCl 2 , Sn and/or SnI 2 , such that the reactivity of free chlorine produced in the discharge is reduced by an excess concentration of tin. Excess tin getters free Cl 2 and 0 2 which are present and also combines with the C1 2 released by dissociation of the SnCl 2 . SnI 2 combines with C1 2 to release less reactive I 2 and aids regeneration of tungsten electrodes. The lamp envelope 2 is of fused silica and the tungsten electrodes 5, 6 are welded to molybdenum leads 9, 10. The spectral emission of the lamp is stated to be similar to that of a black body at 5500‹ K.