Discharge lamp cathode having tip, middle, and body portions

摘要

A discharge lamp includes a cathode and an anode which face each other in an arc tube, wherein the cathode is made of tungsten in which thorium oxide is doped. The cathode has a cylindrical body portion, a tip portion having a cone shape, and a middle portion formed between the body portion and the tip portion, wherein an angle &thetas;1 of the tip portion is set to a range of 55 degrees≦̸&thetas;1≦̸65 degrees, and an angle &thetas;2 formed by side faces of the middle portion is smaller than that of the tip portion.