A How-To Guide on Fluorescent Light Ballast Replacements

Stop fluorescent lights from flickering and humming with a new ballast.

Next Project

An hour or less






Replace the ballast when your fluorescent light flickers or makes an annoying hum. The repair will only take about 10 minutes.

Tools Required

  • 4-in-1 screwdriver
  • Nut driver
  • Wire stripper/cutter

Materials Required

  • New ballast
  • Wire connectors

When your fluorescent light flickers or makes a loud and annoying hum, a degrading ballast is the cause.  Replacing a ballast is different than replacing a light fixture. However, buying a ballast can be expensive, so consider pricing a brand-new fixture for comparison. You can find a new ballast at a hardware store or home center and install it in about 10 minutes.

What Is a Fluorescent Light Ballast?

The ballast takes in electricity and then regulates current to the light bulbs, stabilizing the output of the light. In other words, this is what makes the light stay lit. A fluorescent light has to have a ballast in order to work, without it, the current would increase as it passed through, ruining the lamp all together.

The good news is that a typical ballast will generally last about 20 years, so you won’t have to worry about replacing them very often. However, cold environments and bad bulbs can factor into the mix, causing the lifespan of the ballast to decrease significantly. There are several different types of ballasts, and they’ll say how many lamps they can regulate at once as well as what kind of lamps they’re compatible with.

Replace the fluorescent light ballast in four steps.

Project step-by-step (4)

Step 1

Remove the Bulbs and Fluorescent Light Fixture Cover

  • Unplug the fixture or turn off the power at the main panel.
  • Remove the fluorescent ballast compartment cover to expose the internal wiring and ballast.
    • Note: The attachment method for ballast covers varies widely among manufacturers. It may be attached with nuts or clips or simply snapped into place.

Fluorescent lightsFamily Handyman

Step 2

Cut the Old Ballast Wiring

  • Snip the old fluorescent ballast wiring several inches from the end of the fluorescent ballast with side-cutting pliers or wire snips.
  • Cut all the wires connected to the fluorescent light ballast.
    • Note: There will be four to eight wires coming out of the ballast.

Step 3

Unscrew the Old Ballast

  • Unscrew the ballast- mounting nut and drop the old ballast free.
    • Note: The ballast will have either one or two mounting nuts.
  • Hold onto the ballast with your free hand to keep it from falling out.

fluorescent light

Step 4

Install the New Ballast

  • Mount the new ballast in the fixture.
  • Strip the electrical wiring back 1/2 inch and connect the matching-colored wires with twist-wire connectors.
  • Replace the ballast compartment cover and bulbs.

Buying a New Ballast

Take the old ballast to the store with you. Compare the new and old ballasts to verify that the wiring diagrams, voltage and current match before installing the new ballast.