Patent ID: 8274227

Claim:
A ballast arrangement for a lighting fixture mountable in different orientations in a suspended ceiling system having a DC power supply, comprising: a pair of DC input terminals connected to the DC power supply with a predetermined polarity in one orientation of the fixture, and with a reverse polarity in another orientation of the fixture; an automatic polarity protection circuit connected to the DC input terminals for supplying an output DC voltage of constant polarity no matter in which of the orientations the fixture is mounted; a main DC ballast circuit including a main DC ballast powered by the output DC voltage from the protection circuit to enable a lamp in the fixture to be illuminated during normal operation; and an emergency back-up DC ballast circuit to enable the lamp in the fixture to be illuminated during emergency operation upon failure of the DC power supply, the emergency back-up DC ballast circuit including a battery charged to a charged DC voltage by the output DC voltage during the normal operation, and an emergency DC ballast powered by the charged DC voltage from the battery to enable the lamp in the fixture to be illuminated during the emergency operation.