How to Test a Fluorescent Light Bulb

A woman installs a light bulb.
  • 1 hours
  • Beginner
  • 80
What You'll Need
Continuity tester

Chances are that you have a fluorescent light bulb, if not a handful of them, in your home. Fluorescent light bulbs are the most popular bulbs available in the market nowadays. The reason for that fame is because they’re extremely compact, produce plenty of light, and are energy efficient. However, there comes a time when a fluorescent light bulb and its corresponding light fixture exhibit certain glitches like excess flickering before light up, turning on then off suddenly, or not lighting up at all. During such scenarios, it is important that the homeowner test the light bulb and see if it is broken or if the fixture is.

Step 1 - Check the Electricity

One reason why your fluorescent bulb might not be functioning properly is that there’s no electricity to power it. To know if this is the case, check your circuits. You can find them in the electrical service panel and see if any of the circuit breakers are turned off.

Step 2 - Inspect the Bulb’s Appearance

If power isn’t the problem, the next step is to visually inspect the bulb’s appearance. To do this, you will have to take the fluorescent bulb out. Before you even attempt to unscrew the bulb, make sure to turn off the circuit breaker connected to the light fixture. Wait for a few minutes to let any electricity left in the lines dissipate. To remove the bulb, twist it while carefully guiding the electrodes. Most light fixtures will have small openings near the electrodes to help you unscrew the bulb out easier. When you get the light bulb out, visually inspect its appearance. Discoloration often suggests that the bulb is close to getting busted.

Step 3 - Test the Bulb in Other Fixtures

If you do not notice any kind of discoloration, then maybe the problem is not with your bulb. To verify, simply install the bulb in another light fixture. If it lights up, then the problem is with your original fixture. If it doesn’t light up, then it must really be your bulb. If you don’t have access to any other light fixture, use a continuity tester for the electrodes.

Step 4 - Check the Starter

The problem with some old light fixtures is that they have worn out starters. The starter is that small box or cylinder in the fixture that’s positioned near the bulb. The starter feeds your bulb with a high-voltage charge. A very common symptom of a starter problem is when your bulb flickers for a long time before lighting up. In this case, remove the starter from the fixture and replace it. If that doesn’t work, try replacing the starter with a new one.

Step 5 - Check the Ballast

In the event that with a new bulb and new starter the fluorescent bulb still won’t light up, your best bet is to check the ballast. With a screwdriver, take out the ballast and survey it for any oil leaks. Install new ballast if the current one is leaking oil. If it isn’t, try to check the system for any loose connections.