A ballast is an electrical device that regulates current in a circuit, most commonly used to control the current to arc-based light sources such as fluorescent or HID (high-intensity discharge) lamps.
Ballasts ensure arc-based lighting systems operate safely and efficiently. Light sources such as fluorescent, mercury vapor, metal halide, and sodium lamps require high voltage to start and then limited current to maintain. Without a ballast, these lamps would draw excessive current once the arc is established, leading to overheating or failure. Ballasts provide the starting voltage and regulate current to safe levels. In commercial and industrial environments, they stabilize performance, reduce power fluctuations, and protect wiring. Available as magnetic or electronic devices, modern electronic ballasts are preferred for energy efficiency, reduced noise, and compatibility with advanced controls.
Ballasts are subject to standards from UL (Underwriters Laboratories), DOE (U.S. Department of Energy), and IEEE. Their efficiency is also regulated under U.S. Energy Policy Act and lighting efficiency standards.
Ballasts were first developed in the early 20th century with gas-discharge lighting. Early versions used inductive magnetic coils, which were bulky and noisy. The late 20th century introduced electronic ballasts, aligning with energy efficiency initiatives and the need for dimmable, programmable lighting systems.