| 摘要 |
PURPOSE: To provide a short arc type mercury discharge lamp with which an arc is formed and maintained along the axis of the electrode and devitrification and burst of arc tube are prevented due to secure formation of discharge generated between electrodes along the electrode axis at start up time of a lamp. CONSTITUTION: Within the arc tube 1 of the short arc type mercury discharge lamp, a cathode 2 and an anode 3 are arranged and the cathode 2 has a tapered section 22 on which a sloping face 21 is formed and mercury and a gas are enclosed in the arc tube 1. When the weight of mercury per unit volume within the tube is n (mg/cm¬3) and the pressure of the rare gas is (kPa) at a room temperature (25°C), n and p are respectively 0.2<=n<=52 and 0.1<=p<=800. For the cathode 2, a protruded section 23 is formed as a continuation of the tapered section 22.
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