| abstract |
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/cm2) 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 (μm) is the crystal grain diameter of the polycrystalline alumina ceramic. |