| 摘要 |
PROBLEM TO BE SOLVED: To provide a discharge lamp having a long lifetime and excellent stability while reducing the wear of a tip of an electrode even in longtime lighting by specifying a diameter of an electrode made of tungsten including the rare earth compound. SOLUTION: A negative electrode 3 and a positive electrode 6 are arranged opposite to each other in a bulb 5 made of the quartz glass surrounding a discharge space having an electrode diameter set at 1 mm or more in the case of 50-150 W of lamp input, at 2 mm or more at 150-1000 W, and at 5 mm or more at 1000 W or more, and the electrodes are arranged with a space at 2 mm. As a material for the negative electrode, 2 wt.% of La2O3-W is used, and as a material for the positive electrode, pure W is used. Since a function of work is smaller than that of a thorium tungsten electrode, operating temperature can be lowered, and the electrode material temperature can be set at a recrystallization temperature (1500 deg.C) or less except for a range in which the electrode material contacts with an arc, and the deformation range of the electrode becomes the minimum, and wear of the electrode tip part is restricted so as to prolong the lifetime, and since the deformation range of the electrode tip is small, arc is stabilized.
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