a first converter circuit that converts an input voltage into a desired voltage in accordance with a control signal generated by a power control unit based on at least one of a voltage of a lamp and a current of said lamp;

a second converter circuit that converts said desired voltage into lamp supply voltage in accordance with a drive control unit, and provides said lamp supply voltage to said lamp; and

a starter circuit coupled between said second converter circuit and said lamp, said starter circuit generating a starting pulse to start said lamp,

wherein said lamp has a substantially low mercury level,

wherein said power control unit performs said control by one of pulse width modulation and pulse frequency modulation,

wherein said first converter circuit converts a DC input voltage into a desired DC voltage, and said second converter circuit converts said desired DC voltage into an AC voltage; and

wherein said power control unit includes a time constant circuit comprising a capacitor and a resistor, the time constant circuit operating when a difference between the lamp voltage and a reference voltage reaches at least a threshold value, and a charge time constant of the capacitor is switched in accordance with one of an increase of said difference and an increase of a voltage of the capacitor to control a temporal change rate of the electric power during a transient time period in a stepwise manner,

wherein said power control circuit comprises:

a voltage change detecting unit that detects a difference between a reference voltage and said lamp voltage, and outputs said difference;

an electric power controller that receives said difference, said lamp voltage and said lamp current, and generates said control signal

wherein said electric power controller comprises:

a first control unit that generates a first output current that is substantially constant when said difference is within a predetermined voltage range of reference values;

a second control unit that generates a second output current that increases temporally until said lamp reaches a stable lighting state, wherein said temporal increase is based on one of an increase in said difference and a time lapse, wherein said temporal increase is one of continuous and stepwise; and

a third control unit that generates a third output to control said lamp voltage and said lamp current during said stable lighting state,

wherein said first control unit and said second control unit control said lamp voltage and said lamp current until said lamp reaches said stable lighting state.