| 摘要 |
PROBLEM TO BE SOLVED: To provide an image reading device capable of prolonging furthermore the life of a halogen lamp. SOLUTION: By sending a current into a halogen lamp 32, tungsten 136 is evaporated from a heated filament 132 and bonded with halogen gas 134 to form tungsten halide 138. A halogen cycle, that the tungsten halide 138 is decomposed again and the tungsten 136 adheres to the filament 132, is repeated. At this time, as a gas concentration of the halogen gas enclosed in a glass tube 130 is reduced beforehand corresponding to a working voltage lower than a rated voltage, acceleration of corrosion of the filament 132 caused by reaction of excessive halogen gas 134 with tungsten 136 composing the filament 132 does not occur. Therefore, in case that a working voltage lower than a rated voltage is used, the life of the halogen lamp 32 can be prolonged furthermore.
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