A lamp contains a voltage conversion circuit that converts a line voltage to an RMS load voltage and includes a switch and a microcontroller that operates the switch to define the RMS load voltage. The microcontroller senses a load voltage of the lamp, compares the sensed load voltage to a reference RMS voltage, and operates the switch in response to the comparison so that the RMS load voltage is substantially constant at the reference RMS voltage over an operating range of the line voltage and so that the RMS load voltage decreases with decreasing line voltage at line voltages less than the operating range. The operating range of the line voltage is defined to have a minimum that is a non-zero line voltage at which a load current is a predetermined maximum. The voltage conversion circuit may be a phase clipping circuit or a pulse width modulation circuit.