| 摘要 |
PROBLEM TO BE SOLVED: To improve light flux rise and a dark point by sealing a first amulgum in a narrow pipe, providing a second amulgum sealed inside a transparent discharge vessel having a specified diameter or less at a position apart form the first amalgam, and making a discharge passage length specified or more. SOLUTION: In a transparent discharge vessel 1 whose diameter is 18 mm or less and discharge passage length is 300 mm or more, a communication part 1b is formed at a position backward toward one side from the other side of a linear part 1a by a blow-off method and arranged in an H shape. Narrow tubes 3A, 3B are integrally formed with a flare stem 1c while they are communicated with the inside of the vessel 1, and an end thereof projecting outward is sealed. A first amulgum 6 is sealed in the narrow tube 3A. A second amulgum 6 is fixed to a seal part on the other end in the vessel 1. Since a most cooled part is formed at the end of the vessel 1 so that mercury vapor is fed to the other end of the vessel 1 from the second amulgum 6, no dark point is generated.
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