an incandescent lamp that is filled with a mixture of inert gas and a halogen (usually iodine or bromine) and operates on the halogen cycle, that is, the process of reverse transfer of tungsten onto the filament, from which it evaporates. Because of the formation of gaseous compounds of tungsten and halogens at temperatures above 3OO°-400° C and their decomposition near the surface of the filament, the precipitation of tung sten particles onto the walls of the bulb is eliminated. This makes possible a considerable reduction in the dimensions of the bulb or lamp without risk of a large decrease in light flux during its service life. The bulb is composed of hard quartz glass; heating the bulb up to 600°-700° C during operation ensures high pressure of the filling gas for the period of burning. Iodine lamps have smaller dimensions and considerably higher luminous efficiency than ordinary incandescent lamps with identical power and service life; they are widely used in various optical systems and light instruments.
V. M. SKOBELEV