PURPOSE:To prevent a rise in lamp voltage and the extinction of a lamp by using a metallic material, whose surface is made of a nickel plated layer, as a supporting member for a luminous tube. CONSTITUTION:When a metallic material with a nickel plated layer is used for as a supporting member 11 for a luminous tube, a group CHX impure gas generated in an outer tube 9 during performance is quickly decomposed by a catalyst action of nickel. A carbon layer generated by decomposition is formed concentratively on both end parts of the luminous tube where the supporting plates 11 for the luminous tube are situated, and so the amount of ultraviolet radiation from the luminous tube 1 is small. A H2 gas generated concurrently due to decomposition of the group CHX gas can be absorbed by a getter material 12 with absorptive capability to H2. Hence, disappearance of sodium does not occur, so that a rise in lamp voltage and the extinction of the lamp can be prevented.
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