How to Replace a Light Ballast

fluorescent lights
  • 1-3 hours
  • Beginner
  • 0-300

A ballast is the material in a fluorescent light bulb that regulates the current that goes into the actual lamp. It provides the correct amount of voltage to get the lights to turn on without allowing too much electricity to flow through. For this reason, they are often called control gears. Over time, these ballasts can wear out and cause lamps to stop functioning correctly, and they could even potentially influence other structures within the light system.

Learn when and how to replace a light ballast from the tips below.

Step 1- Observe the Light

When a ballast starts to go, the light source will dim steadily each time it is activated and shut off, and eventually it won't come on at all. As it slowly loses the ability to channel power to the lighting device, the ballast will cause other aspects of the light device to work less effectively too. If you observe this happening in your fluorescent bulbs, proceed to the next step.

Step 2 - Determine the Cause

It's simple to figure out why a fluorescent or high-intensity light is not working correctly, since both fail for the same reasons as an incandescent. These include a loss of electrical power, a diminishing ballast, a dead inductor, or a malfunctioning bulb. Check the main power source for the house and see if the circuit breaker has been tripped or a fuse has blown. Make sure the lamp is plugged into a functioning electrical outlet, and then check for damage to the bulb itself.

If the bulb is the source of the problem, it will not light at all. If the ballast is causing the problem, the light will illuminate for a few seconds, then dim slowly and fade out. Turning off the light and turning it on again will repeat this cycle.

Unfortunately for fluorescent lights that develop a random or steady flicker, you also need to rule out all these causes before replacing the light ballast. A flickering fluorescent light tube or bulb can accelerate the failure of the ballast, so don't delay in investigating a light that has begun to flicker in your home or office.

Step 3 - Check the Fluorescent Bulbs

light ballast

If the bulb has become significantly dark and opaque at one end, it is reaching the end of its useful life. Test the circuit across the pins mounted in the end of each long fluorescent tube. The electrodes are functioning properly if a current can cross the gap between the pins. A loss of inert gas in the bulb will also cause a loss of illumination. These aren't issues that can be repaired, and will require a replacement. Even in a light fixture that uses a pair of fluorescent tubes, replace both when one fails.

If a tube fails again within a month after a replacement has been made, then that could indicate a problem with the ballast.

Certain areas require that old or broken fluorescent bulbs be brought to recycling centers. So, be sure to look up your local laws and dispose of your waste properly.

Step 4 - Decide to Replace or Discard

If your fluorescent light fixture is more than 15 years old, it's a safer bet to replace the entire fixture. At that age, the specific bulbs and ballasts that would serve as replacements for your model may not even be sold anymore.

If it's fewer than five years old though, buy a new ballast and replace the failing one.

Step 5 - Replace the Ballast

Disassemble the fluorescent light fixture to find the ballast, a small metal box with colored wires coming out both ends.

Examine the circuit diagram inside the light housing and detach it. One ballast will operate each pair of bulbs in the light fixture. Purchase a magnetic or electronic ballast, by comparing your old ballast with it at the lighting or building supply center, and install it according to the diagram.


Be careful when you open up the fixture. Fluorescent bulbs are breakable, and while health experts have determined the harmful substances these bulbs contain are negligible if a healthy adult is exposed to a broken bulb, the mercury inside of them can affect children and pets adversely.