Resistor-aided starting of metal halide lamps

摘要

A metal halide high-intensity discharge lamp for connection to a constant wattage-type mercury ballast including a transformer having a secondary winding having a capacitor in series circuit arrangement therewith. The lamp includes starting aid means and warm-up assistance means to ensure reliable operation. The starting aid means is a voltage doubler comprising a diode and two resistors operating in conjunction with the ballast capacitor and also including a normally closed heat-responsive switch means operative to prevent voltage stress on the diode after the lamp starts. The warm-up assistance means comprises a resistor in series circuit arrangement with the arc tube and a normally open heat-responsive switch means connected in parallel circuit arrangement with the resistor so that during lamp warm up, the resistor reduces the phase shift between the voltage of the lamp and the open circuit voltage of the ballast, thereby increasing the maximum sustaining voltage to the lamp when the lamp current is zero, to prevent the arc from extinguishing.