Patent ID: 6492772
Filing Date: 2002-12-10
Classification: H01J

Abstract:
A high pressure discharge lamp comprising:a discharge tube having a discharge chamber that contains a light-emitting substance and is hermetically sealed; and a pair of electrodes, each of-which has first and second ends and is set in the discharge chamber, the first end of each electrode being secured to the discharge tube and the second ends of the electrodes facing each other at a predetermined distance in the discharge chamber, wherein discharge takes place between the second ends of the electrodes, each electrode comprising an electrode rod with a tip and a covering material, the electrode rod and the covering material being made mainly of tungsten and the tip positionally corresponding to the second end, wherein the covering material covers an outer surface of the electrode rod near the tip, the tip being left uncovered, and the tip of the electrode rod and an adjacent portion of the covering material are fused together by heat generated during an initial discharge, and wherein an inequality 1/50*R3&lE;&Dgr;L&lE;1/5*R3 is satisfied before the initial discharge takes place, where &Dgr;L is a length of the tip measured along a direction of a length of the electrode rod and R3 is an outer diameter of the covering material adjacent to the tip.