Abstract: An apparatus and method for supplying emergency power to a lighting device, in particular, an HID lamp, when a failure occurs in a main power supply. The apparatus can include a rectifier circuit for converting an AC voltage signal provided by the main power supply to a DC voltage signal. A capacitive element can be coupled across the DC output terminals of the rectifier circuit and across a DC coil of a DC relay circuit. The amount of energy stored by the capacitor controls the DC relay to provide the voltage of the main power supply to the lamp circuit under normal conditions, and the voltage of an emergency power supply to the lamp circuit when the voltage of the main power supply falls below a predetermined level. Alternatively, an AC relay can be coupled directly to the main AC voltage power supply or emergency power supply and configured to perform a similar operation.