AUTOMOBILE DISCHARGE BULB AND AUTOMOBILE HEADLIGHT

PROBLEM TO BE SOLVED : To provide an automobile discharge bulb having an excellent build-up of luminous flux and luminous efficiency, whereby thermal shock resistance in a ceramic tube can be alleviated. SOLUTION : This discharge bulb is equipped with an arc tube 11A in which electrodes 15a, 15b are provided face to face and a luminescent material is filled together with a starting rare gas in the inside of the ceramic tube 12, and the cross section of the ceramic tube 12 is longitudinally formed. Since an enclosed space s in the ceramic tube 12 is small, and the enclosed space is immediately heated to high temperatures after the discharge starts to cause a good build up of luminous flux, and since the surface area of the ceramic tube 12 is small, a tube wall load (W/square centimeter) rises to cause good luminous efficiency. In this ceramic tube 12 having the longitudinal cross section, a big contact of an arc having a convex shape in its upper part with the tube wall is avoided, thermal shock resistance characteristics required for the ceramic tube are alleviated, and the durability of the ceramic tube is enhanced. In addition, the ceramic tube 12 can be structured by a ceramic material which has not been conventionally usable.