Abstract: A lighting control apparatus to provide variable intensity light from high pressure discharge lamps using two high pressure discharge lamp loads connected in series to provide more widely variable intensity of light. The outputs of two ballasts may be connected in series to feed the series connected discharge lamp load. Preferably a feedback signal proportional to load current is used to stabilize operation. In addition, circuitry is preferably provided to maintain a predetermined minimum current to prevent extinguishing of the lamps from low current and "hot restrike" circuitry is provided to limit the maximum load voltage when the lamps are extinguished.

Abstract: Lighting control apparatus for controlling the light intensity of high-intensity-discharge (HID) lamps operated from an AC source while eliminating the tendency for such lamps to extinguish during the dimming thereof. The apparatus comprises a variable reactive ballast controlled with respect to its reactance by a solid-state switching device which is responsive to a timed control signal provided by a signal generating device operating from the same AC source. A lamp voltage sensing device develops a feedback signal which varies in accordance with the voltage drop across the lamps being ballasted. A signal sensing and overriding device combines the feedback signal and the timed controlled signal and causes the feedback signal to override the timed control signal before the lamp voltage reaches such value as might cause the lamp to extinguish.