Fluorescent ballasts and compact fluorescent (CFL) ballasts install into compatible lighting fixtures to protect fluorescent and CFL 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 the bulbs and then regulate the current to the bulbs for as long as they are on. Dimmable ballasts are compatible with lighting controls that allow a fixture's light output to be dimmed, and non-dimmable ballasts are compatible with lighting controls that turn lights on or off but do not dim their light output.