Patent ID: 8174199

Claim:
A discharge lamp lighting apparatus comprising: a power control circuit that outputs a DC current; an AC conversion circuit to which the DC current is inputted, the AC conversion circuit repeatedly reversing the polarity of the DC current between a first polarity and a second polarity at predetermined timings to produce and output a discharge lamp driving AC current, the driving AC current defining a plurality of AC cycles, each of which includes current of the first polarity and current of the second polarity; and a controller that controls the AC conversion circuit and the power control circuit, the controller controlling the AC conversion circuit to perform AC conversion control in which the timings at which the polarity of the discharge lamp driving AC current is reversed are controlled, the controller controlling the power control circuit to perform section current control in which the magnitude of the DC current is controlled in accordance with a periodic pattern in each of polarity reverse timing sections to control the ratio of accumulated energy supplied to each electrode of the discharge lamp in the first half of the polarity reverse timing section to that in the second half of the polarity reverse timing section, and the controller controls the power control circuit to change the ratio of accumulated energy over the plurality of AC cycles such that the ratio of accumulated energy in a polarity reverse timing section of one AC cycle is different from the ratio of accumulated energy in a polarity reverse timing section of another AC cycle.