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Fluorescent Light Troubleshooting

Troubleshooting fluorescent lights is relatively easy; however, it helps to have some simple skills with electrical components. Fluorescent lighting and incandescent lighting are terms some people use interchangeably, but they are not the same thing. These two fixtures use different mechanisms. In a fluorescent bulb, mercury particles emit ultraviolet light. A heated filament creates the visible light in an incandescent bulb.

If you are uncertain where to start troubleshooting, here is a guide to follow. You can start by checking the power supply, bulbs, bulb retainers, and then the ballast.

Power – Tracking the flow of power to the lamp is a systematic process. A good safety tip is to use a non-contact voltage tester. This device is a tool that quickly and safely checks for electrical currents.

  • First, go to the breaker box. Use a noncontact voltage tester to make sure the circuit breaker is on, and power is present in the output wire of the fixture.
  • Then, remove the cover off the light switch and use the tester to check for electrical energy there. Put the switch cover back on and turn on the light.
  • Lastly, remove the fixture cover and again use the tester to check there for power. If energy is present at each of these points, you can move on to checking the bulbs.

Bulbs – If the end of the bulb has a dark area, replace it with a new one. If the fixture is a two or four bulb fixture, replace the tube pairs. If the bulbs all work, but the light still does not, check the bulb retainers.

Bulb retainers – Though uncommon, the bulb retainer can cause problems in your light fixture. The brass spring clips located inside the lamp can break.

  • Check by rotating the damaged bulb into its clips. You should feel a definite stop when the electrodes engage.
  • If there is no forced stop, replace the clips because they are weak. Clips also need to be replaced if you notice any burn spots on them.
  • You can also turn the light switch on and use the non-contact voltage tester with each clip. Then test the clips with the light turned off.
  • Use the tester to check the continuity for each clip through the ballast’s output wire. If there is no continuity, replace the clip.

Ballast – This delivers a high voltage that is needed to light up the bulb. It also provides current control to prevent bulbs from excessive current draw. If no other components listed above are causing the issue, the ballast is the problem. It usually costs more to replace the ballast than to buy a new light fixture.

Common problems with fluorescent lights

There are several common issues that owners face with light fixtures. Common indications are dead or flickering lights, buzzing or humming sounds.

Dead or flickering lights

If your light fixture has dead or flickering fluorescent bulbs, it could be due to

The bulb – This is the most familiar problem with fluorescent light fixtures. Look for a dark area at the end of the bulb. If there is one, the bulb is defective or is going bad.

The starter – This is a small, gray metallic cylinder. It plugs into the socket located on the fixture’s frame. Usually, fixtures that are less than 15 years old do not have a starter.

The ballast – This is the transformer component of the fixture.

Buzzing lights

Most home fixtures with fluorescent lighting use magnetic ballasts and operate at about 60 hertz. This operation can create a buzzing sound. You can replace the magnetic ballast with an electronic one if you have the thinner, more modern fluorescent tubes (also called T-8’s). The electronic ballast operates at 20,000 - 40,000 hertz continuously. This change will eliminate the buzzing sound.

Humming lights

Usually, a humming sound is caused by the bulb’s prongs getting misaligned or dirty. First, take out the bulb and wipe the prongs clean. Then inspect the prongs to make sure they are not bent. Use a pair of pliers to straighten bent prongs. Put the bulb back in. If it still hums, try reinserting the bulb but flip the ends around. If this does not fix the problem, then it may be caused by the starter or ballast.

Replacing parts

After troubleshooting the fluorescent light and it still does not work, you may need to replace parts. The most common replacements are the bulbs, ballast or starter.

Replacing the ballast

To replace this component, you will only need a combination stripper, screwdrivers (that will fit the screws on the light fixture), and your voltage tester. Replacing the ballast in some models may cost more than replacing the whole unit.

  1. Turn power off to the circuit. Double-check that electricity is not going to the light by using your voltage tester.
  2. Take off the tube and the cover plate that covers the mechanisms. Keep the screws in case your new ballast does not come with any.
  3. Disconnect the wires that go to the ballast and remove. If you choose, take a picture of the wiring that is there. This option will aid you later as a reference in how to wire your new ballast.
  4. Strip off some insulation from the wire ends (about a half inch).
  5. Install the component and attach the wires with wire nuts.
  6. Add the cover and tube.
  7. Reactivate the circuit.
  8. Switch the light on again.

Replacing the starter

With older models, you may need to replace the starter.

  1. Shut the light off at the switch.
  2. Take off the tube.
  3. Move the starter a quarter turn clockwise and remove it.
  4. Plug the new starter in and move it a quarter turn counter-clockwise.
  5. Put in the tube.
  6. Turn on the light switch.


Following a maintenance schedule could prolong the life of your fluorescent lights.

  1. Periodically inspect your fluorescent lamp to check for bulb discoloration, high temperatures, dimming lights, inoperative fixtures, and dust or dirt.
  2. Replace your lamp when it reaches about 80% of its expected life.
  3. Clean lenses and fixtures periodically to prevent accumulation of dirt or other debris. If debris collects, it can later impede the light’s ability to turn on.

Tubes last longer than ordinary incandescent light bulbs, making them a preferred lighting option. Troubleshooting fluorescent lights can be a simple process if you have the right information. Usually, repairs are easily fixed with DIY solutions. If you have any questions regarding lighting, ask an Expert. 

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