| 摘要 |
PROBLEM TO BE SOLVED: To lengthen the service life, and restrain flickering of a lamp by supplying a direct current on which a ripple frequency falls within a specific range and a ripple rate is not more than a specific value, to a metal halide lamp having a pair of electrodes having a specific interelectrode distance. SOLUTION: Metallic halide is sealed in a light emitting tube 20 as light emitting metal, and rare gas such as mercury and argon as buffer metal is sealed. An interelectrode distance is not more than 6mm, and a direct current is supplied from a DC source 40, and it is lighted. In order to restrain flickering of a lamp by a ripple component superimposed on the direct current, a ripple frequency of the direct current is restricted to a range of 35 to 55kHz, and a ripple rate is restricted to 15% or less. It is desirable that the sphere ratio of a metal halide lamp is not more than 1.0 to 2.0 and a tube wall load is 40 to 100W/cm<2> . |
