| 摘要 |
PROBLEM TO BE SOLVED: To provide a discharge lamp in which the transition from glow to arc is promoted and an arc discharge is stabilized over a long time. SOLUTION: A fluorescent lamp 1 has mixed gases of argon gas and mercury vapor sealed therein by sealing heat cathodes 4, to which Dumet wires 3 are connected, to both ends of a glass bulb 2 in such a manner that the heat cathodes 4 are opposite to each other. The heat cathode 4 has a plurality of granules stored in a bottomed cylindrical cup 6, the diameters of the granules being 10 to 100μm. The cup 6 and the granules 7 are composed chiefly of barium-tantalum-oxide with a small amount of zirconium oxide and are covered on their surfaces with thin films of tantalum carbide in order to enhance sputtering resistance. The cup 6 is held coaxially with respect to a holder 12 made of nickel. The holder 12 has a pawl part 15 formed to project toward an opening 11 in an end and is oppositely located each other above the opening 11 while facing the granules 7, the end 17 of the holder 12 preventing the axial movement of the cup 6. A phosphor 25 is applied to the inside of the glass bulb 2.
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