PURPOSE: To keep high the maintenance factor of luminous flux by keeping the tube wall of an arc tube away from portions where temperature is high so as to restrain the temperature rise of the tube wall, and restraining reaction of quartz glass with a metal halide so as to prevent devitrification of the quartz.
CONSTITUTION: A floodlight 60 is used with the optical axis O2-O2 of its reflector 2 pointed in a roughly horizontal direction, and a short arc metal halide lamp 1 is horizontally lighted. The lamp 1 is connected to a DC power supply 50 and lighted by DC while the load on a tube wall is as high as 63W/cm. In this case, devitrification of the wall of a light emission tube can be prevented by satisfying I/D 0.6A/mm wherein the lamp current is IA and the maximum bore of the arc tube 20 in the direction perpendicular to a line connecting electrodes 21, 22 is Dmm. Since the wall of the light emission tube is kept away from an arc by I/D being 0.6 or less, the temperature rise of quartz is restrained and thus the rate of reaction of the quartz with the metal halide is reduced.
FURUYA MAMORU
TANAKA ICHIROU
