Ballast for high pressure sodium lamps having constant line and lamp wattage

A constant line and lamp wattage ballast for high pressure sodium lamps, comprising:

• a direct current source that generates pulses of direct current;
• a lamp circuit, having a voltage, that is interconnected with, and receives direct current pulses from, said direct current source, said lamp circuit including,
• a high pressure sodium lamp, and
• an inductor interconnected with said lamp;
• ambient light sensing means for sensing the magnitude of ambient light present near said lamp;
• a striker circuit interconnected with a high voltage induction coil, said striker circuit being adapted to generate a high voltage signal to strike said lamp when both the magnitude of the ambient light sensed by said ambient light sensing means is below a predetermined value and said lamp is not lit;
• an undervoltage protector means for sensing the lamp circuit voltage, comparing it with a predetermined value, and extinguishing power to said lamp if the circuit voltage is less than the predetermined value;
• a current feedback means for sensing the current present in the said lamp circuit, comparing said current with a reference value, and generating an output signal;
• a pulse width modulator that, in response to said output signal of said current feedback means, varies the width of said direct current pulses;
• a high frequency oscillator;
• a switch that gates direct current pulses to said lamp;
• and
• a switch control means, responsive to said oscillator, for controlling said switch and thereby controlling the frequency of said direct current pulses that power said lamp.