Abstract: Circuit operating from a direct current source applies DC pulses to a high pressure sodium vapor lamp to improve the color rendition of the lamp. The circuit includes a first inductor, a diode and a capacitor connected across a DC source, and a second inductor, controlled thyristor switch and sodium vapor lamp connected in series across the capacitor, and a timing circuit for periodically turning on the switch at predetermined intervals. The circuit provides for charging the capacitor, commutating the controlled switch, and discharge of the capacitor to enable subsequent re-charging thereof, so as to povide the desired pulsed operation of the lamp. This mode of operating also provides for application of voltage to the lamp which is substantially higher than the supply voltage.

Abstract: Electrical ballast circuit for operating gaseous discharge lamps with direct current. An inductive reactor coil connected to an alternating current source is connected to a discharge lamp via a full-wave rectifier, and an auxiliary induction coil inductively coupled to the reactor coil is connected to the discharge lamp via another full-wave rectifier, resulting in the currents from the respective rectifiers to the lamp being out of phase with one another, thereby raising the average current through the lamp and the voltage across the lamp to prevent lamp de-ionization and reduce lamp re-ignition voltage. Series connected capacitors may be incorporated in the circuit to increase the starting voltage on the lamp if necessary.

Abstract: Color rendition of high pressure sodium vapor discharge lamps is improved by disclosed operating circuit for applying pulsed direct current to the lamp. The circuit includes a direct current ballast circuit having a low ripple factor, a filter capacitor charged by the output of the ballast circuit, and a pulsing circuit comprising a transistor switch which operates to apply DC pulses on the lamp at a predetermined repetition rate and duty cycle to provide desired color properties of the lamp.