| 摘要 |
PROBLEM TO BE SOLVED: To provide a light emitting tube for a discharge lamp by which a reduction in linear transmissivity is reduced and which has the long lamp service life since corrosion of an inner wall surface of a light transmissive tube can be restrained by forming the light transmissive tube to constitute the light emitting tube for a metallic vapor discharge lamp, out of light transmissive ceramics on which a pore occupying rate is not more than specific % and an average pare diameter is not more than a specific value. SOLUTION: A light emitting tube 1 for a metallic vapor discharge lamp such as a metal halide lamp, is formed by sealing a light emitting material composed of metallic halide and rare gas inside an almost cylindrical light transmissive tube 2 having a curved surface-shaped projecting part 2a in the center, and opening parts 2b and 2c on both ends of the light transmissive tube 2 are sealed with glass 4 by a blocking-up body 3 made of a cermet material. Light transmissive ceramics to constitute the light transmissive tube 2 are formed of a material on which a pore occupying rate is not more than 0.3%. and an average pare diameter is not more than 3.6μm.
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