Patent ID: 7443103

Claim:
A ballast for operating a gas discharge lamp comprising: means for supplying an alternating lamp current, said alternating lamp current comprising a mean amplitude I 1 and alternating half cycles, each half cycle occurring during a time period T; and means for generating one or more current pulses in the later half of time period T, said one or more current pulses comprising a mean amplitude I 2 and a time duration of Tp, wherein a current ratio Ri is equal to or greater than 2.0, where Ri=I 2 /I 1 , and a duration ratio Rt is equal to or greater than 0.2% and equal to or less than 5% or in the alternative, equal to or greater than 15% and equal to or less than 50%, where Rt=Tp/T, wherein the alternating lamp current and the one or more current pulses are combined, and wherein the leading edge of the one or more current pulses commences after a time delay Td from the trailing edge of the half cycle of the alternating lamp current.