METAL HALIDE LAMP

摘要

A metal halide lamp comprising an arc tube which has a pair of electrode leads having an electrode at its end, a main tube portion having therein a discharge space where the electrodes are opposed to each other and made of a polycrystalline alumina ceramic, and a pair of thin tube portions through which the electrode leads are passed and which are connected to the main tube portion and sealed with a sealing material. The following relations are satisfied: 20<=WL<=50, EL/Di>=2.0 and 0.5<=G<=5.0 WHERE WL (W/CM<2>) is the tube wall load of the arc tube, EL (mm) is the distance between the electrodes, Di (mm) is the inside diameter of the main tube portion, and G (mum) is the crystal grain diameter of the polycrystalline alumina ceramic.