Life and luminous flux of halogen incandescent lamps related to filament temperature, pressure and CH2Br2 content

Abstract

An experimental study has been made of 20 V, 100 W halogen incandescent lamps using different filling pressures for the halogen additive (0. 25-16 torr CH2Br2) and the inert gas Kr (4-16 atm.), and burning at two voltages. The maximum luminous flux and life were found for lamps with halogen filling pressures of 1-4 torr CH2Br2. Lamps with low halogen filling pressures blacken. At high pressures, attack on the cold coil ends determines life. The blackening or non-blackening in general accords with the transport criterion derived from the solubility of tungsten in the gaseous phase. Halogen lamps with properly operating transport cycles fail due to a local temperature increase leading to burning-through of the filament. The experimentally found relation between life, filament temperature and filling pressure agrees approximately with the theory of the radial transport of tungsten in these halogen lamps. A correlation was found between lamp life and the temperature increase of the hot spot.