| 摘要 |
PROBLEM TO BE SOLVED: To suppress blackening caused by electrode scattering and to improve the luminous flux maintenance factor of a lamp by adding Sb or its halide into an arc tube in addition to rare gas and a halide of Sc. SOLUTION: The internal capacity of an arc tube 11 is 0.025 cc, and Xe is sealed at 7 atm and at the ordinary temperature as starting gas into the arc tube 11 in addition to a metal halide 16. The metal halide 16 is added with SdI3 and NaI of 0.45 mg in total and SbI3. The lamp voltage is sharply increased when SbI3 is added although no mercury is contained. The lamp current can be suppressed as compared with the conventional metal halide lamp, a thermal load to an electrode 13 is reduced, thus blackening can be suppressed, and the luminous flux maintenance factor can be improved. If the added quantity of SbI3 is about 2 mg/cc or above, the lamp voltage becomes 50 V or above.
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