Patent ID: 8581510

Claim:
A lighting device for a discharge lamp comprising: a direct current power source; a down-converter circuit configured to step down a direct current voltage supplied from the direct current power source; a polarity inversion circuit configured to receive an output voltage from the down-converter circuit and apply the output voltage to the discharge lamp with a polarity of the output voltage inverted periodically; a resonance circuit configured to generate a starting voltage for starting up the discharge lamp; a control circuit configured to control the down-converter circuit, the polarity inversion circuit, and the resonance circuit to control lighting of the discharge lamp; a voltage detector configured to detect the output voltage from the down-converter circuit configured to step down the direct current voltage; a detector configured to detect a state of output of the polarity inversion circuit; an output voltage determiner configured to determine the output voltage from the down-converter circuit on a basis of the output voltage from the down-converter circuit detected by the voltage detector and the state of output of the polarity inversion circuit detected by the detector; and a lighting detector configured to detect lighting and extinction of the discharge lamp, and detect whether a current in the discharge lamp is in an asymmetric state during a period of detecting lighting of the discharge lamp, wherein the control circuit reduces the output voltage from the down-converter circuit when the asymmetric state is detected by the lighting detector.