Abstract: An exit illuminating system for illuminating an exit or exit sign with high intensity light under emergency conditions, the light having sufficient brilliance to be visible through smoke in order to lead persons who may be trapped in the smoke-filled area to the escape exit. The system incorporates an emergency condition detector responsive to power failure, smoke and heat in order to develop an activating signal which energizes a high intensity xenon flash lamp. The system is made fail-safe by a circuit which causes a battery to power the flash lamp if line power is lost and which keeps the battery at full charge when external power is available.