Standard fluorescent lighting fixtures are more energy-efficient than incandescent light fixtures, and the bulbs generally last considerably longer, but occasionally a special transformer inside the fixture, called a ballast, may need replacing. The type of ballast in the fixture will depend on the age of the light fixture.
On newer fixtures or those that have been updated, the ballasts are electronic and are more energy-efficient and quieter than older-style magnetic ballasts. They are also much less prone to problems. But older fluorescent fixtures use magnetic ballasts, and these can go bad. Magnetic ballasts are those that tend to hum when the lights are on, and when they go bad, they can drip a tar-like black substance down into the fixture. If your lights flicker or turn themselves off—and you're sure it's not due to bad tubes or bad sockets—it's time to replace the ballast.
Be sure to find a replacement ballast with the same wiring configuration and voltage rating as the original. Choose an electronic ballast, if available. Also, compare the cost of the ballast vs. a new fixture; sometimes it's a better investment to replace the entire fixture.
Equipment / Tools
- Non-contact voltage tester
- Smartphone or digital camera (optional)
- Wire cutter
- Nut driver or socket wrench
- Wire strippers
- Replacement ballast
- Wire connectors (wire nuts)
Turn Off the Power
Turn off the power to the circuit containing the light fixture by switching off the appropriate breaker in your home's service panel (breaker box). If the fixture has a cord and plug, simply unplug it to disconnect from power.
- Note: Simply turning off the light switch controlling the fixture is not an adequate way to turn off the power to the fixture. Always turn off the circuit breaker controlling the circuit powering the light fixture.
Remove the Cover
Remove the lens, or diffuser cover, from the fixture. Some fixtures have a clear plastic lens that wraps around the outside of the fixture. On these, grab the outer edge and gently pull the cover away from the fixture and down. If the fixture has a lens inside of a framed lid, look for locking clasps that pull down and allow the lens to swing down.
Remove the Fluorescent Tubes
Remove the light bulbs (fluorescent tubes). Grab the bulb and twist it about 90 degrees until you see the metal contacts at its ends. Gently pull down on one end, so the contacts slide out of the socket and remove the bulb from the fixture. Repeat the process for the remaining tubes.
Now is a good time to inspect the sockets holding the tubes at each end of the light fixture. If they are loose or broken, they should be tightened or replaced.
Remove the Cover Plate
Locate the wiring cover plate, usually in the center of the fixture. On either side of the cover, there will be tabs that catch in slots in the fixture. Squeeze the sides of the cover inward to slip the tabs out of the slots, and pull the cover down. This will expose the ballast and its wiring.
Disconnect the Ballast Wires
Look for the black wire and white wires connected to the ballast. These are the power source wires. Before touching any wires or wire connections, confirm that the power is off by testing each wire with a non-contact voltage tester. The test should indicate that there is no voltage present in the wires.
In addition to the source wires, there may be four or more wires connecting the ballast to the fixture's bulb sockets.
- Tip: Take a photo of the ballast and wiring for reference when installing the new ballast.
Disconnect all of the ballast wires by removing the wire connectors and separating the wires, or, if necessary, cutting the wires close to the ballast using a wire cutter.
Remove the Ballast
Support the ballast with one hand (to prevent it from falling) and remove its mounting nut(s) or bolt(s) with a nut driver or socket wrench. Remove the ballast from the fixture. Bring the ballast with you to the store to find a suitable replacement.
Prepare the Wires
If you had to cut the wires earlier, or if the wire ends are damaged, strip about 1/2 inch of insulation from the end of each of the fixture wires, using wire strippers.
Mount the New Ballast
Mount the new ballast to the fixture, using the mounting nut(s) or bolt(s). Connect the ballast wires to the fixture wires to match the original wiring, using wire connectors. Reinstall the wiring cover plate, the light bulbs, and the fixture lens. Restore power by switching on the circuit breaker and test the fixture for proper operation.
Dispose of the Old Ballast
Dispose of the old ballast, following the recommendations of local authorities for proper disposal practice.
Older fluorescent light ballasts (those manufactured before 1979) likely contain polychlorinated biphenyls (PCBs), classified by the EPA as an environmental toxin. If these ballasts are leaking, they should be regarded as hazardous waste and treated very carefully. Avoid skin contact with the tar-like substance inside a ballast. The best strategy is to take all old ballasts to your nearest hazardous waste disposal site or to consult local authorities for instructions on how to dispose of them.