| 摘要 |
PROBLEM TO BE SOLVED: To provide a lighting device that can optimally maintain the protrusion shape and tip shape of an electrode for a long time to extend the service life of a discharge lamp.SOLUTION: A lighting device lights a high pressure discharge lamp having a discharge container made of quartz glass in which a pair of electrodes are arranged facing each other and a mercury is enclosed. The lighting device supplies alternating current so as to alternately generate alternating current at steady-state lighting time with frequency (basic frequency) selected from a range of 60 to 1000 Hz, and alternating current of a low frequency at a half-cycle with a frequency lower than the basic frequency; supplies alternating current so that a waveform of one polarity of the low frequency appears two times or more; and when switching polarities of the electrodes, controls so that the value of the low frequency gradually approaches to the value of the basic frequency. This allows tungsten to be alternately melted and deposited between one electrode and the other electrode so as to optimally keep the protrusion shapes of the electrodes. |
