Abstract: A tungsten halogen lamp is provided that incorporates therein means for reducing the lower operating temperature limit of the halogen cycle operating within the lamp's envelope. In addition, there is provided a halogen lamp fill gas mixture, which is comprised of an inert gas, a halogen or halide and a phorphorus-based compound and a carbon-containing compound that will reduce the lower operating temperature limit and greatly increase the efficiency of the halogen cycle, thereby allowing operation of a tungsten halogen lamp at temperatures about or below 400.degree.-500.degree. K. The compounds in the fill gas mixture have a phosphorus-to-carbon mass ratio of about 10:1 to about 1:1.

Abstract: A tungsten-halogen lamp is provided that incorporates therein means for substantially reducing filament embrittlement. The embrittlement reducing means comprises substances X and Y, which have an X and Y mass ratio of about 30:1. Substance X is a phosphorus-based gaseous compound and substance Y is a carbon-containing gaseous compound. Substance X is preferably phosphine and substance Y is preferably methyl bromide.