HID is an abbreviation for high intensity discharge and it describes several families of lamps that rely on arc tubes constructed from quartz or ceramic to produce light. These arc tubes are pressurized above normal atmospheric density and generally have a protective outer envelope surrounding them for safety purposes. The arc tube is filled with different combinations of inert gas and chemical compounds to produce the desired light spectrum and optimal level of illumination. These lamps fall into two broad categories, metal halide and high pressure sodium with the metal halide lamps available in a much greater variety of sizes and shapes. All HID lamps require a ballast to deliver proper electrical current for the lamp to operate and the ballast must be matched to the lamp type by wattage, arc tube construction and ignition style. Generally, the lamp and ballast combinations are not interchangeable and some the lamps will only operate in specific positions so correct product identification is very important. Please do not hesitate to contact a Kelsun sales representative for assistance with any HID requirements.