ELECTRIC DISCHARGE LAMP OPERATING DEVICE

An electric discharge operating device operates an external electrode fluorescent lamp (13) using a rare gas by applying high frequency voltage from a high frequency power supply circuit to external electrodes. The pressure of the rare gas in the external electrode fluorescent lamp (13) is more than 120 torr. The frequency of the lamp current supplied to the external electrode fluorescent lamp is in the range from 24 kHz to 34 kHz. The external electrode fluorescent lamp (13) is operated at high luminance without flickering, and no flickering occurs even in dimming. The drive frequency of the fluorescent lamp (13) is in the range from 24 kHz to 34 kHz producing no audible noise in high dimming rate operating modes including a 100% dimming rate operating mode. In a low dimming rate operating mode a semiconductor switching elements (S1, S2) are driven so that the frequency of the fluorescent lamp (13) is in a low frequency range from 20 kHz to 24 kHz. Thus in a high dimming rate operation, the lamp is operated stably with high luminance without contraction of the positive column of the lamp.