Ballasts are power supplies or transformers for fluorescent lamps, light sources that consist of a glass tube filled with argon, neon, or other inert gas. When ballasts supply electrical current, the resulting arc emits ultraviolet (UV) radiation that excites the phosphors inside the lamp wall, causing them to radiate visible light. Basic lighting ballasts can be as simple as a series of resistors – a common configuration in small neon lights. Other types of ballasts include electronic ballasts, magnetic ballasts, fluorescent ballasts, high intensity discharge (HID) ballasts, and metal halide ballasts. Ballast manufacturers are located across the United States and around the world. They adhere to a variety of standards, including guidelines from organizations such as the American National Standards Institute (ANSI).