HID lamp is a kind of high pressure discharge lamp, its discharge of the "volt" performance is negative resistance characteristics, so in the lamp working circuit need to connect the current limiting device, that is, commonly known as ballast. Most of the HID lamps work in the AC state, using the reactance device as the ballast. HID lamps have different types, according to the type of lamp and its application needs, can be configured in different forms of ballast circuit, in order to obtain the best match between ballast circuit and lamp. As commonly used in general lighting HID lamps have high-pressure mercury lamps, high-pressure sodium lamps and gold halide lamps. High pressure mercury lamp is the earliest development of the HID lamp light source, product performance is stable, supporting ballast circuit is more mature. High-pressure sodium lamps and gold halide lamps are modern development of high-efficiency energy-saving new light source, requiring ballast energy and lamps have a good match, in order to achieve better comprehensive results.