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. HID ballasts are used in outdoor lighting fixtures like wallpacks, area lights, and parking lot lights or indoor industrial fixtures such as high-bay lights or temporary jobsite lights. ANSI codes are assigned to HID light bulbs and ballasts, and bulbs and ballasts with the same codes can be used together.