| 摘要 |
PROBLEM TO BE SOLVED: To obtain a long service life of a light source from a high-pressure discharge lamp by restricting the relationship between a radius and a lamp current of a tungsten bar constituting an electrode by means of a specific formula and restraining the blackening at the initial life stage. SOLUTION: In a high-pressure discharge lamp in which electrodes 2a and 2b are arranged opposed to each other inside an arc tube 1 so that the spacing length L between them may be 3mm and which is lit by means of a power supply whose polarity is reversed, when the radius at the tip end part of each electrode is r mm, the lamp current during ordinary discharge is I ampere, and the ratio of the circumference of a circle to its diameter isπ, the relationship of 1.5<=(I/π<=r<2> )<=9 is met. A light emission tube 1 is roughly rotary elliptic- shaped, and indium iodine InI, holmium iodine HoI3 are sealed as a sealing material, and mercury as a buffer gas and argon as a startup rare gas are sealed.
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