| 摘要 |
PROBLEM TO BE SOLVED: To provide an ultrahigh pressure mercury lamp which is small in size, high in radiant intensity and also high in color rendering property and also provide a high-efficiency ultrahigh pressure mercury lamp which does not cause nonevaporation in a bulb portion even when the amount of mercury enclosed is high and scarcely causes blackening or the like of the bulb portion due to wear of electrodes even when a distance between the electrodes is shortened to make an electrode load great. SOLUTION: For the ultrahigh pressure mercury lamp comprising a discharge container composed of a substantially ellipsoidal bulb portion made of a transparent material and side bulb portions connected to and contacted with the bulb portion, a positive electrode and a negative electrode arranged oppositely to each other in the discharge container, and mercury enclosed in an amount of 0.2 mg/mm<SP>3</SP>or greater into the discharge container, and subjected to DC lighting at input power of 400 W or lower, the relationship between the length D of the tip portion of the positive electrode to the length L in an axial direction of the lamp bulb of the bulb portion satisfies D≥L/2. COPYRIGHT: (C)2004,JPO
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