Gas discharge lamp control

Abstract

The input energy to a gas discharge lamp is controlled over a given range to obtain output light regulation in a controlled fashion for different kinds of gas discharge lamps, including fluorescent lamps, high intensity discharge lamps and others associated with any type ballast, including conventional non-dimming type ballasts. A suitable circuit switches each half wave of an input a-c wave form from some instantaneous value greater than zero to a substantially zero value and then back to a value greater than zero one or more times in each half cycle. The time duration of the substantially zero energy interval is varied to vary the total energy applied to the gas discharge lamps. In a preferred embodiment, a first high speed electronic switch is connected in series with the a-c source and lamp ballast and a high speed electronic shunt switch is connected across the a-c line and ballast input. The series switch is opened to produce the zero energy interval. Simultaneously with the opening of the series switch, the shunt switch is closed to allow discharge of energy stored in the reactive components of the ballast into the lamp. When the series switch is reclosed, the shunt switch is simultaneously opened. Other embodiments are described which include the use of passive energy divertors in place of the shunt switches or across the series switch. Numerous protective circuits protect the control circuit, the lamp and ballast, and the a-c line.