| 摘要 |
PROBLEM TO BE SOLVED: To perform the judgement of the end of life of a discharge lamp before the discharge lamp starts lighting. SOLUTION: The lighting device comprises a discharge lamp 1 that is controlled of lighting by a lighting circuit 2, a current detecting means 10 for detecting the current flowing in the filament electrodes of this discharge lamp, a voltage detecting means 11 for detecting the voltage between the filament electrodes, an A/D conversion means 12 that makes digital conversion of the detected value from each detecting means, a memory 15, and a CPU that controls drive of the lighting circuit. The CPU calculates the filament resistance value by taking in the detection value of the current and the voltage from the A/D conversion means immediately after the start of preheating control, and stores this in the memory as a resistance value Rc. Then, in the preheating period after that, the CPU takes in the detection value of the current and the voltage at certain intervals and calculates the filament resistance value Rh, and by obtaining the ratio Rh/Rc of this resistance value Rh to the resistance value Rc stored in the memory, stores it in the memory. Then, when the difference of the two succeeding ratios exceeds a certain value, it judges the end of life of the discharge lamp. COPYRIGHT: (C)2004,JPO |
