| 摘要 |
PURPOSE: To prevent the blackening an internal surface of an arc tube by quickly sufficiently evaporating a metal or metal compound condensed in a root part and an exhaust chip of an electrode which are a low temperature part of the arc tube, to shorten a rise up time also to improve lighting efficiency, and suppressing wearing due to a discharge of the electrode. CONSTITUTION: A pair of electrodes 2, 3, mercury and/or rare gas are sealed in a quartz-made arc tube 1, to provide a visible light permeating doping layer 7 in an internal surface or a total area of this arc tube 1. When assumed T1 for thickness of the arc tube and T2 for weight concentration of a doping layer relating to weight of an arc tube total unit, a value of T1 /T2 is specified in a range from 8.0×10<-3> to 6.9×<-1> .
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