HID ballast kits contain HID ballasts, capacitors, ignitors, and other parts that are used to maintain HID light fixtures. They save time compared to buying the components separately, and they make sure users have the parts on hand that they need to replace an old ballast and its coordinating components. HID ballasts are used with lighting fixtures that use metal-halide or high-pressure-sodium HID light bulbs. They protect light bulbs from damaging power fluctuations that can reduce the quality of the bulbs' light output. They provide an initial spike of high voltage to turn on light bulbs and then regulate the current to the bulbs for as long as they are on. ANSI codes are assigned to HID light bulbs and ballasts, and bulbs and ballasts with the same codes can be used together.