How to check if the ballast is bad in fluorescent lighting

Updated February 21, 2017

If there is a flickering or buzzing sound coming from your fluorescent light fixture, you may have trouble. The inside of a fluorescent tube has a component called a ballast. The ballast is an electrical connection that holds the fluorescent bulb in place and supplies the electricity that makes the chemicals inside the bulb ignite. The ballast also regulates the flow of electricity properly so that there is no flickering. Test your ballast if there is humming, flickering or the light doesn't turn on.

Turn off power to the fluorescent light fixture by unplugging it or shutting off its fuse. Allow the fluorescent light to rest for a while before working on it to allow any remaining electricity to discharge.

Twist the fluorescent bulb so that it releases from the light fixture. Inspect the fluorescent bulb for black marks or loose parts that indicate the bulb itself is faulty.

Unscrew the protective cover from the end of the ballast and examine the exposed end for signs of oil. Oil leaks indicate that the seal inside the ballast is broken and that this component needs to be replaced.

Turn the voltmeter to the Ohms setting and touch one probe to the white wire and the other probe to one of the coloured wires. You should get a reading of a short or a continuous circuit. The ballast is damaged and needs to be replaced if there is no short or continuity.

Replace the damaged or faulty ballast with a new unit, twist the fluorescent bulb back into the light fixture and turn the power back on. If the light fixture still hums, flickers or does not work properly, you may have to replace the bulb, as well.

Things You'll Need

  • Screwdriver
  • Voltmeter
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