Q&A

The lighting ballast is a device that regulates the starting and operation of lamps by acting as a positive resistance to the current. Lamps often have a negative resistance, so without the ballast they would continue to draw current until the power supply failed. There are many types of ballast; the type used depends on the type of lighting.

Fixed resistors are used as ballasts in neon lamps with small loads, and increasingly in LED lights; this negates any negative resistance of the lamp. Variable resistors can be used for ballasts in incandescent lamps; they maintain a constant current through the ballast despite changes in resistance to the rest of the electrical circuit.

To limit the power lost through resistors, a reactive ballast is used for lamps larger than around 2W. These ballasts are also known as magnetic ballasts and contain inductors and sometimes capacitors (to improve the power factor) and can power fluorescent or high intensity discharge (HID) lamps.

Electronic ballasts use electronic circuitry to regulate the starting and operating conditions of fluorescent and HID lamps. These act to change the frequency of power drawn from the mains to 20kHz, eliminating flicker. These ballasts are usually smaller, lighter and more efficient than magnetic ballasts.