| 摘要 |
PROBLEM TO BE SOLVED: To prevent that an acoustic resonance phenomenon occurs, even at a changed lighting frequency or changes of lighting frequency and occurrence of an acoustic resonance phenomenon are repeated frequently. SOLUTION: While a detection means 19 is not detecting the acoustic resonance phenomenon of a high-intensity discharge lamp 18, a control device 14 keeps the output frequency of the high-frequency generator 10 at the upper limit in a prescribed frequency region; while when the detection means 19 detects the acoustic resonance phenomenon, the control device 14 changes the output frequency of the high-frequency generator 10 in the low direction. Since the high-intensity discharge lamp 18 has the characteristics that the frequency for generating acoustic resonance phenomenon becomes low, accompanied by the increase in the lamp voltage at the initial stage of lighting, changing the output frequency of the high-frequency generator 10 in the low direction means that it is in a relation of avoiding the change in the frequency that generates the acoustic resonance. COPYRIGHT: (C)2008,JPO&INPIT |
