| 摘要 |
PROBLEM TO BE SOLVED: To provide a metal halide lamp with little fluctuation of illuminant color at lamp lighting in spite of a fluctuation of power supply voltage or of ballast output, or variation of lamps at manufacturing. SOLUTION: A light-emitting tube 1 is contained in an outer tube 3 provided with a metal base at its one end. The light-emitting tube 1 is formed in oval sphere with quartz glass and has at least several kinds of metal halide (mainly, sodium halide and cerium halide) and a rare gas sealed as light-emitting materials. On the outer surface of each end of the light-emitting tube 1, a heat- insulating film 14 is formed consisting of zirconium oxide or the like so as to cover an electrode sealing part 11 and the surroundings of an electrode 2. Each of the outer tube 3, heat-insulating film 14, and a sleeve 12 has the role as a coldest point temperature maintenance means for maintaining the coldest point temperature of the light-emitting tube 1 at 600 deg.C or higher when lit at lowest usable lamp voltage against the rated lamp power.
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