Patent ID: 7397191
Filing Date: 2008-07-08
Classification: H01J

Abstract:
1. High pressure discharge lamp, comprising: a bulb; an opposed anode and a cathode in said bulb, the cathode having a cylindrical body part and a conical part which is doped with thorium dioxide (ThO wherein, between the body part and the tip area of the conical part, at least one light receiving surface area is formed at a base part of the conical part, the at least one light receiving surface area extending in a plane which intersects a center axis of the conical part which passes through the tip area of the conical part and the body part, wherein an angle, which is formed between the plane and the center axis and which is measured from a side of the body part, is greater than an angle of inclination which is formed between the outer periphery of the conical part in the tip area of the conical part and the center axis; and wherein said at least one light receiving surface area comprise a plurality of step-shaped areas arranged in succession in the manner of stairs on the conical part, a step surface of a step of each of the step-shaped areas facing in a direction toward the tip area of the conical part so as to absorb radiant heat from a discharge arc formed between the cathode and anode.