| 摘要 |
A metal halide lamp has an arc tube that includes: a pair of electrode structures, each of which has an electrode at a tip; a main tube part made of polycrystalline alumina ceramic, and containing a discharge space in which the electrodes of the electrode structures are located to oppose each other; and a pair of thin tube parts that connect from the main tube part and are sealed by respective sealing members with the electrode structures inserted therein, where 20≤WL≤50, EL/Di ≥ 2.0, and 0.5≤G≤5.0 are satisfied where tube wall loading of the arc tube is WL(W/cm<2>), a distance between the electrodes is EL(mm), an inner diameter of the main tube part is Di(mm), and a crystal grain diameter of the polycrystalline alumina ceramic is G( mu m). <IMAGE>
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