China manufacturer of magnetic ballasts for metal halide flood lights & hps flood lights

Negative resistance characteristics of sodium lamps, that is to say, those lights working current increases, the lamp resistance but reduced. Unlike the incandescent lamp, the lamp current is increased, the filament resistance also becomes large. Also unlike the constant resistance, the current increase does not affect the resistance value. Sodium lamp with ballast, in order the stable sodium lamp operating current, because the sodium lamp is also negative resistance characteristics. You think if no ballast, when the sodium lamp operating current increases, cause lamp resistance becomes small, light resistance becomes greater and greater and the lamp current. Continue to do so, simply can not be stabilized sodium lamp. Therefore, you must use the current limiting devices. The high pressure sodium ballasts are a large inductance, it is inductive impedance in AC, thus limiting sodium lamp operating current.