How To Test A Fluorescent Light Fixture

15 February 2017
 Categories: , Blog


If you have a dead or flickering fluorescent light, test it before you replace it. Many issues with fluorescent lights are caused by the ballast and bulbs, but it may be any number of things.

Older lights operate by ballast only, while newer lights made after 2000 use a starter and ballast. You should be able to do this test yourself. Here are tips to test a fluorescent light fixture.

Prepare to Work

For this project, you need:

  • screwdriver
  • starter ballast
  • multimeter
  • working flourescent light

Ensure power is getting to the light. Run a voltmeter over the breaker box to check for current. Look for tripped breakers. If a current is detected, shut off power to the fixture from the breaker box, and let the light cool.

Replace the Starter

Flickering bulbs could indicate a problem with a starter, a small cylinder or box on one of the fixture's ends. Bulbs made before the year 2000 use them.

Replace the starter. It should twist out of the socket. Reinsert the new starter; pressing it firmly in the connectors. If a new starter didn't fix the problem, troubleshoot the bulb.

Troubleshoot the Bulb

Detach the cover from the fixture with the screwdriver, and set the screws aside. Gently unscrew the light bulb, guiding it from the two electrodes, and ensure they aren't bent or missing. Some fixtures may have two screws on the electrodes to make removing the bulb easier.

A U-shaped bulb attaches by springs. The bulb should come off when you pull up.

Check each bulb end for a dark color. A dark color indicates failure. Try the bulb out on a working flourescent fixture., If the bulb works, the problem is the other fixture.

Test the Ballast

If the light stays on for several seconds, then dims, the problem is the ballast. Test the ballast for continuity. Detach the ballast cover, if there is one. Remove the screws with the screwdriver.

Set the multimeter to ohms (omega symbol: Ω) on the lowest setting or X1K on multimeters with various settings. Attach one probe to the white wire connector and another probe to the ends of the blue, white, and yellow wires. Some fixtures may only have red or blue wires.

Check the needle on the multimeter. If the ballast is faulty, the needle won't move. A needle moving to the right indicates a good ballast.

A digital multimeter will display a number. A reading between 0.5 and 1.2 ohms indicates a good bulb, Any other reading is a sign of a faulty ballast. Replace the ballast, and test the fixture again.

Testing  a fluorescent light is uncomplicated. If the light still doesn't work, contact an electrician.