A switched preconditioner circuit is provided at the power input end of a light source to effectively drop the voltage of the light source to zero volts whenever the light source is required to be in an OFF state thereby eliminating the problem of unwanted current through the light source. The preconditioner circuit may include a terminal connected to a first power potential, a terminal connected to a power node at the power input end of the light source, and an input to receive a preconditioner control signal to place the preconditioner circuit in one of an ON state and an OFF state. The preconditioner circuit supplies the voltage to the power node in its ON state and effectively eliminates the voltage to the power node in its OFF state. The preconditioner circuit also may include a bleed path connected between the power node and a second or ground potential to shunt all power supplied to the power node when the preconditioner circuit input receives a signal to place the preconditioner circuit in the OFF state.