The ARC keeper: Eliminates nuisance lamp outages created by short duration line disturbances. Allows a metal halide fixture to operate as an emergency light source (when used in conjunction with a generator). Is available in models for use with pulse-start and probe start lamps. Maintains the lamp arc for up to two minutes, providing sufficient time for a generator system to respond to the loss of normal power or for a minor line disturbance to pass. Powers the lamp at approximately 25% of the lamp’s wattage rating during transition to generator support. Is suitable for indoor and damp locations. (Outdoor fixtures may be served by the ARC keeper if the device is remote mounted.). Distinguishes between a deliberate lamp shutoff and a power failure. Works with a constant-wattage auto-transformer (pulse- and probe-start models), high reactant auto transformer (pulse-start models) or reactor style (pulse-start models) magnetic ballast. Substantially reduces concern over lamp re-strike and downtime.