Each time the processor computes a correction term, y(n), in the lamp current control loop, it will compute another term in accordance with the equation PW ( n ) = K * y ( n ) V VF , where PW(n) is proportional to the pulse width or duty ratio of the inverter switch, K is a scaling constant, VVF is the sampled value of the valley-fill bus voltage, and n is an integer index indicating one of many s