Lighting power supply

A lighting system power supply arrangement comprising a mains input converter operable to provide power and is operable to charge an energy storage device, a controller operable to control at least one element of the lighting system, a controller bus and a controller interface operable to provide control signals from the bus to the lighting system, and an isolated DC-DC auxiliary converter operable to power the lighting system from the bus, wherein the controller bus carries power for the purpose of conveying the control signals, and wherein the auxiliary converter is operable to use said power to power the controller from the bus and is operable to power the lighting system when the mains input is outside normal operating values.