Home Electrical: How To Repair A Flourescent Light Fixture

Fluorescent light fixture repair is easy if you undertand how they work.

Fluorescent light repair is a simple task if you understand the terminology and follow a simple method of troubleshooting.

Fluorescent light fixtures come in various sizes and shapes. The fixtures may vary in construction, but they operate in the same way. The operation of a fluorescent fixture is accomplished by exciting a gas, at a high voltage, in a sealed glass tube. Once the gas is excited or illuminated, the voltage is then reduced and the gas continues to give off light by the rapid movement of the gas molecules.

The parts may vary in a fluorescent light fixture, but the actual components are all generally the same. Below is a list of the common parts that make up the fixture.

Fluorescent tubes - These are the actual sealed bulbs that contain a gas. This gas, when electrified, emits light from the colliding gas molecules. You should exercise extreme caution when handling these bulbs. They are under a small amount of pressure and they can explode if broken. The glass is very fragile and very sharp.

Tombstones - The fluorescent bulbs fit into these small plastic holders called tombstones. They contain small metal contacts that conduct the electricity to the fluorescent tube or bulb.

Starter - The starter is a small cylindrically sized relay that helps to jumpstart the bulb, by applying a high voltage to the tombstones. Older fluorescent fixtures still employ this type of relay starter. Many modern fixtures have done away with them and have integrated the starter in to the ballast transformer.



Ballast transformer - The ballast transformer is the heart and soul of the fluorescent light fixture. This device creates the high voltage that is required for igniting the gas inside the sealed tube. Some larger fixtures may contain two of these transformers, especially for a fixture that may hold four or more bulbs. There are two sets of wiring that lead to and from the ballast transformer. The primary wires carry the line voltage, either 120-vac or 240-vac. The secondary wires carry the voltage to the tombstones from the ballast.

A simple method of troubleshooting the fluorescent light fixture is described below in the order of repair. Generally, three symptoms show that there is a problem with a fixture: The lights are completely out, one bulb is only burning or the bulbs are flickering

1. Are the bulbs themselves loose or burned out? You can perform this simple test with the power still applied to the light fixture. Carefully, twist the bulbs using both hands, to see if they are seated in the tombstones properly. If they are in a proper seat, then the bulbs may be burned out. Replace all bulbs in the fixture. A weaker bulb will draw more power and affect the ballast transformer with poor performance.

2. The bulbs are new and still no lights are burning. Disconnect all power to the light fixture before proceeding. Once the power is shut down, carefully remove the bulbs and the main cover. You should see the complete wiring and ballast transformer under the main protective cover. Check all wiring connections from the primary to the ballast transformer secondary wiring, and the tombstones. Check, the wiring into the tombstone connectors, sometimes the small wire will work loose inside the connector.

If all of the wiring connections check to be fine, you should then be sure that you are receiving the proper line voltage. Remove the wire nuts from the primary wiring, exposing the main power wires. Position the exposed wires in such a way so they will not short against each other or the fixture. Reapply power and check the voltage reading on a Multi-meter. If you have the proper voltage reading, shut the main power off and check the starter.

3. If the fixture is an older model, there maybe a small cylindrical relay starter. Replace this starter, reapply power, and reinstall the bulbs.

4. If none of the above troubleshooting methods has corrected the problem, you have come to the only, final conclusion: the ballast transformer is faulty. Replacement of the ballast transformer is not difficult. All ballast manufacturers include a systematic guide for their own particular models. You may want to shop around for prices on the particular model. Some manufacturers may expect a heavy price for their product. In some cases, you may find it is less expensive to replace the entire fixture compared to the replacement cost of a new ballast transformer.

5. Some discount stores sell four-foot fluorescent fixtures so inexpensively, that they are almost impossible to repair economically. These new fixtures do not contain a ballast transformer. They use a small capacitor that does the same job. These small, high voltage-producing capacitors can be more expensive than the original price of the fluorescent fixture itself.

© High Speed Ventures 2011