| 摘要 |
PROBLEM TO BE SOLVED: To prevent a back arc from being generated between a tubular body and an electrode used as an electrode different from the tubular body particularly in restart. SOLUTION: An arc tube 6 is provided with an envelope 17 made of ceramic comprising a main tube 15 and narrow tubes 16 formed at both ends of the main tube 15, and electrode introduction bodies 22 sealed in the narrow tubes 16 and each having an electrode 18 at an end, and the quantity of mercury enclosed therein is not more than 4.0 [mg/cm<SP>3</SP>]. In each narrow tube 16, a metallic tubular body 25 is intervening between the electrode introduction body 22 and the narrow tube 16. When it is assumed that the smallest distance from an opening surface on the main tube 15 side of the narrow tube 16 to the tubular body 25 is Li [mm], a relational expression of 0 [mm]<Li≤0.5[mm] is satisfied. When it is assumed that the smallest distance from the opening surface on the main tube 15 side of the narrow tube 16 to the tip of the electrode 18 nearer to the opening surface and a tube wall load of the arc tube 6 are L<SB>e</SB>[mm] and W<SB>e</SB>[W/cm<SP>2</SP>], respectively, relational expressions of 1.3[mm]≤L<SB>e</SB>and Le≤W<SB>e</SB>/11 are satisfied. COPYRIGHT: (C)2006,JPO&NCIPI
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