| 摘要 |
PROBLEM TO BE SOLVED: To provide an ultrahigh-pressure mercury lamp capable of preventing tungsten constituting an electrode from dispersing in starting it and in lighting it, and of preventing blackening from occurring on an inside wall of an arc tube. SOLUTION: This ultrahigh-pressure mercury lamp is composed by protrusively arranging a pair of electrodes oppositely to each other in the arc tube and by filling the arc tube with mercury above 0.15 mg/mm<SP>3</SP>, a rare gas and halogen. In the ultrahigh-pressure mercury lamp, at least one-side electrode out of the pair of electrodes comprises a shaft part formed of tungsten and a start assisting part; a part of the shaft part is embedded in a sealing part formed continuously to the arc tube; the shaft part or the shaft part and the start assisting part include an easily electron-emitting substance having a work function lower than that of tungsten; and, when it is assumed that the volume of the electrode projecting into the arc tube, the volume of the electrode embedded in the sealing part, and the concentration of the easily electron-emitting substance included in the shaft part or the shaft part and the start assisting part and having the low work function are V1 (mm<SP>3</SP>), V2 (mm<SP>3</SP>) and A (wt.%), respectively, a relationship of 2×10<SP>-3</SP>≤V1/(V1+V2)×A≤4.8 is satisfied. COPYRIGHT: (C)2007,JPO&INPIT
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