ULTRAHIGH PRESSURE MERCURY LAMP AND ITS ELECTRODE

PROBLEM TO BE SOLVED : To provide an ultrahigh pressure mercury lamp used for a long lifetime and high efficiency exposure device etc. by reducing the consumption of an electrode of the ultrahigh pressure mercury lamp used by blinking at a high frequency and to provide its electrode. SOLUTION : The ultrahigh pressure mercury lamp of AC an ignition type includes a pair of cylindrical electrodes oppositely disposed at both ends, and a light emitting tube in which a rare gas is sealed in the tube. When the radius of the tip of the electrode is r, the protrusion-like false circular arc curved surface of a range surrounded by a chamfered curved surface by a circular arc of radius of about r/2 is formed at a corner from a semicircular shape having a radius r to the central part of the electrode tip as a flat surface from the electrode tip to the r in a tubular axial direction.