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...http://www.google.ca/patents/US5955843?utm_source=gb-gplus-sharePatent US5955843 - Relay circuit for providing power from a normal or emergency power supply to ignite and drive a high intensity discharge lamp
