1. A system comprising:a light source;
a converter configured to convert an AC voltage to a DC operating voltage during normal operation;
a power backup device coupled to the converter;
a current source having a first terminal configured to receive the DC operating voltage during regular operation and a second terminal configured to provide a pulse-width modulated (PWM) signal to an anode end of the light source; and
a switching device having a first connecting terminal coupled to the anode end of the light source, a second connecting terminal coupled to the power backup device, and a control terminal coupled to the converter,
the switching device configured to open a switch between the first connecting terminal and the second connecting terminal during normal operation and close the switch upon detecting an interruption of the DC operating voltage at the control terminal.