Control circuit and system for providing emergency lighting

Abstract

A control circuit and system is disclosed for providing emergency lighting from a single source of electrical power which itself is capable of providing input power alternately in the form of a sinusoidal power signal and a square wave power signal during interruption of the sinusoidal power signal. In the preferred form of the invention, a high intensity discharge lamp (HID) and an emergency lamp are provided in the same lighting fixture. A control circuit in the form of a power source detector first detects whether a sinusoidal power signal or a square wave signal is being supplied from a power station onto a pair of input lines. The power station automatically supplies the detector with input power in the form of a square wave rather than the normal sinusoidal power signal when an emergency condition exists such as normal power failure. The detector couples the input power to the HID lamp and the input power is sinusoidal in form and, alternatively, automatically couples the input power to the emergency lamp when the input power is in the form of a square wave.