A ballast configured to connect to a set of lamps to energize the set of lamps is provided. The ballast comprises an inverter circuit for generating an oscillating power signal, wherein the oscillating power signal has a frequency, and a resonant tank circuit electrically connected to the inverter circuit for receiving the oscillating power signal and therefrom providing a lamp current to the set of lamps. A resistance circuit is connected to the inverter circuit. The resistance circuit has a resistance that defines the frequency of the oscillating power signal generated by the inverter circuit. A current control circuit is connected to the resistance circuit for adjusting the resistance of the resistance circuit as a function of a number of lamps that are connected to the ballast.