| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a lighting device which can suppress reduction in an illuminance maintenance rate due to the displacement of a protrusion, thereby helping to extend the life of a discharge lamp. <P>SOLUTION: In a lighting device which lights a high pressure discharge lamp having a pair of electrodes disposed facing each other in a discharge vessel made of quartz glass and also having mercury sealed therein, an AC current is supplied in such a way that an AC current at steadily lighted time of a frequency selected from a range of 60 to 1000 Hz (fundamental frequency) and a low wave cycle of a frequency selected from a range of 5 to 200 Hz lower than the fundamental frequency will alternately occur. The frequency of the low wave cycle is changed corresponding to a change in the discharge lamp lighting voltage, and control is exerted so that a period for which the fundamental frequency is supplied will gradually increase or decrease every prescribed time. As a result, the displacement of a protrusion can be restricted, and reduction in an illuminance maintenance rate can be suppressed, making it possible to extend the life of the light source. <P>COPYRIGHT: (C)2013,JPO&INPIT |
