| 摘要 |
PROBLEM TO BE SOLVED: To enhance rupture tolerance of a short arc discharge lamp, and make its lifetime long. SOLUTION: The negative electrode 2 and the positive electrode 3 are opposingly arranged in a light emitting tube 1 of the short arc discharge lamp. Mercury and rare gas are sealed in the space 21 of the light emitting tube 1. The ratio between the maximum inner diameter a of the spherical face part of the light emitting tube 1 and the whole length c of the spherical face of the light emitting tube 1 is made within the range of 0.42<(a/c)<1.02. The ratio between the maximum inner diameter a of the spherical face part of the light emitting tube 1 and the terminal face external diameter b of the spherical surface part is made within the range of 1.82<(a/b)<3.44. The ratio between a lamp electric power W (W) and a surface area S (mm<2> ) in the light emitting part spherical face part is made W/S<0.3. The distortion of the lamp can be made smaller by satisfying such a relation in the shape of the lamp, and rupture is not caused even if the light is lighted on for a long time.
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