| 摘要 |
PURPOSE:To reduce the temperature difference between filament cathodes and to prevent splashing of emitter due to thermal shocks by making a preheating voltage applied to each hot cathode higher than a discharge heating voltage which is applied to each hot cathode after the starting of a lamp. CONSTITUTION:In a low pressure discharge lamp unit provided with a discharge lamp 1 and a lighting circuit device 10, switches S1a, S1b for a preheater are closed before the starting of the unit and a preheating voltage higher than a discharge heating voltage is applied to each hot cathode 4a, 4b. After the unit is started the switches S1a, S1b are opened and switches S2a, S2b for a lighting heater are closed so that voltage applied to each hot cathode 4a, 4b is switched to a discharge heating voltage With this constitution, the amount of drop of filament voltage after the starting of the unit cancels out the amount of temperature rises due to formation of a cathode spot, thus holding the temperature of each hot cathode 4a, 4b at almost the temperature for preheating. Therefore, thermal shocks are prevented and splashing of emitter applied to coat the hot cathodes 4a 4b can be prevented, whereby the life of the lamp can be extended. |
