Emergency lighting system for gaseous discharge lamps

Abstract

This invention pertains to an emergency lighting circuit that operates with a high pressure, gaseous-discharge lamp and associated ballast. When the gaseous-discharge lamp goes out, after once being ignited, sufficient current is supplied to an incandescent light or lights to maintain illumination to the area normally illuminated by the lamp. The device for providing this current may vary, but generally incorporates a voltage breakdown means that receives higher voltage from the ballast when there is failure of the gaseous-discharge lamp than when the arc therein is struck. A preferred embodiment also lights the incandescent lights during initial warm-up of the gaseous-discharge lamp. The incandescent lights may also be used in a cold environment to maintain the gaseous-discharge lamp sufficiently above an ambient temperature level to make possible initial striking of the arc in the lamp when ambient temperature conditions might otherwise prevent it. Further, half-cycles of ballast output voltages are blocked by diodes and capacitors are used to increase the applied voltage to enhance restriking of the gaseous-discharge lamp in additional embodiments.