How to Test Fluorescent Bulbs

Co-authored by Daniel Stoescu and Hunter Rising

Last Updated: October 27, 2024

A flickering or dead fluorescent bulb can be a nuisance and it may be time to replace it. Before going out to purchase a new bulb, ensure the bulb is the main problem. By checking for surface-level issues, cleaning the parts, and looking at the electronics, you can determine whether you have an easy fix or a trip to the hardware store.

Part 1

Part 1 of 3:

Looking for Surface Issues

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1
Look for dark areas at the base of the bulb. When bulbs age and have been used for a long time, brown spots will appear. If darkness begins to form at the ends of the tube, the bulb may be near its end. While they may still light, they are wearing out and will die soon.
- If the darkness only forms on one end of a tube light, flip the tube so the darkened end is on the opposite side of the fixture.
- If darkness forms on one side of the tube, rotate the tube by 180 degrees from how it used to sit.
The pins of the electrode connect the light bulb to the power source. If the pins are bent or misaligned, use needle-nose pliers to straighten them before returning them to the fixture.

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3
Test the bulb in a working fixture. Remove the bulb from the fixture in question and test it in another lamp. If the problem lies within the lamp, the bulb should work in a separate fixture.^{[1]
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Expert Source

Daniel Stoescu
Master Electrician

Expert Interview. 21 June 2021.}
- If testing tube lights, be sure to test both bulbs even if only one is out. Currents travel between both tubes and either could be causing the problem.^{[2]
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Part 2

Part 2 of 3:

Checking the Electrical Components

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Ensure the circuit is not broken. If the breaker has been tripped, push the switch entirely to the off position, and flip the switch back on. Test the lamp again to see if it lights.^{[3]
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2
Test the electrodes using a multimeter. Using a multimeter will determine if the electrodes still hold conductivity. If the electrodes are not intact, the bulb will not have a current running through it.^{[4]
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Research source} Place the probes on both pins of the tube light to get an accurate reading.
- If there is no reading on the multimeter, the bulbs should be replaced.
3
Replace the starter on the bulb if problems persist. Older fluorescent fixtures will have small metal cylinders called 'starters' on the ends. The starter ignites the gas within the bulb and is crucial for lighting the bulb.^{[5]
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Research source} Many hardware stores will carry replacements for only a few dollars.
- Note the wattage of the bulb to ensure the correct starter is purchased.
- Old starters look no different than new starters, so throw away any starters that have gone bad.

Part 3

Part 3 of 3:

Cleaning the Bulb

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1
Wiggle the bulb in its socket. Rocking the bulb back and forth in small motions can help loosen corrosion and dust that may have gathered near the socket. Clean any leftover residue with a fresh paper towel.^{[6]
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Expert Source

Daniel Stoescu
Master Electrician

Expert Interview. 21 June 2021.}
- Make sure the power is turned off to avoid any electrical damage.
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Wipe the bulb with a cloth soaked in dish detergent. Some bulbs will not light if they are covered in dirt or dust. Remove the bulb and gently use a cloth on the surface. When finished, wipe the soap clean with another cloth soaked in water.
- Be careful handling a fluorescent tube. They’re fragile and have potential to break into shards.
Clear away any corrosion or residue as you rub the pins. Small particles like these restrict the electric current and may be the source of your trouble. Use a cloth or paper towel to remove any loose particles before returning the bulb to the fixture.