| 摘要 |
PROBLEM TO BE SOLVED: To provide a metal halide lamp with no liberation of halogen, less change of elementary light color, and a long life by adjusting the ratio of the sealing amount of holmium halide to that of a halide in the specified range. SOLUTION: The both ends of a transparent alumina tube 1 are sealed with an electrically conductive disc 2 and a glass frit. The disc 2 is obtained by forming a metal coating 5 on the surface of a ceramic base body 4. The disc 2 has an electrode 6 at its one end, and a ceramic insulating body 7 for preventing a back arc is fixed to the surface of the metal coating 5 on the electrode 6 side. Iodides of holmium, thulium, dysprosium, sodium, thallium, and caesium, mercury, argon gas, and metal holmium are sealed in an arc tube in the specified ratio. When the amount of halide sealing material is represented by A micro mole, and the sealing amount of metal holmium is represented by B micro mole, the relation of 1.3<=(B/A)×100<=19 is satisfied.
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