| 摘要 |
PROBLEM TO BE SOLVED: To provide a discharge lamp which can restrain an amount of thoriated tungsten used and is excellent in arc stability and longer lifetime. SOLUTION: In the discharge lamp having an anode 4 and a cathode 5 inside a discharge vessel 1, the cathode 5 is made up from a thoriated tungsten section 7 with a tungsten filling ratio of at least 90% and a main body section 6 connected to the thoriated tungsten section 7 and made of pure tungsten. A ratio S<SB>T</SB>/S of a side surface area S<SB>T</SB>of the thoriated tungsten section 7 to a side surface area S of the cathode 5 is in a range of 0.005 to 0.15. Here, the side surface area S of the cathode 5 is used for calculating the ratio S<SB>T</SB>/S, and a distance of the cathode 5 from an anode side front end is to be up to twice the maximum diameter of the cathode 5. COPYRIGHT: (C)2011,JPO&INPIT
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