| 摘要 |
PROBLEM TO BE SOLVED: To provide a high pressure discharge lamp having a lamp tube 1 in which, a pair of electrodes 2A, 2B facing each other, are inserted, and at least mercury and halogen gas are enclosed, with few blackening and deterioration in brightness even after lighting for a long period, and protected from gas leakage and lamp tube explosion. SOLUTION: A partial pressure of oxygen in a lamp tube in which, halogen gas with a prescribed density is enclosed, is made less than the partial pressure possible to keep the brightness at 80% after the use for 100 hours, and more than 1.0×10<-5> Pa.
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