High intensity discharge (HID) lighting, by definition, has high levels of electrical discharge, to create an electrical arc in the bulb, which emits light. Supplying the power to create, drive, and sustain this arc reliably is no easy feat. The device that does this is called a ballast. It is a complex circuit made up of many components to accomplish specific tasks. To sum it up, one could say that the ballast is a "power controller" in an HID system.