Why Does Only One Fluorescent Light Bulb Work? (Find Out Now!)

Ryan Womeldorf
by Ryan Womeldorf

Fluorescent lighting is a popular choice in many styles of building. It is a cheap, effective way of providing lighting. That said, there are times where seemingly all but one of the bulbs stop working altogether.

There are a few common reasons that it would stop working. It could be as simple as the other bulbs being bad, but that’s not the most common reason. It is more likely that the ballast is broken. You will have to replace the ballast if you don’t replace the light entirely. There is also a chance that it could be the light starter though most new fluorescent lights don’t have starters.

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Troubleshooting a Fluorescent Light

When your fluorescent light stops working, it can be a frustrating experience. Thankfully, there are a few steps that can be taken to properly troubleshoot the issue. The most common issues are flickering, buzzing, or some/all of the lights failing to light.

Does not light. Test to make sure that all of the bulbs are seated properly. Sometimes it can be as simple as tightening the tubes to make sure they seat properly. If that does not work, the tubes could be bad. Check them with a voltage detector or multimeter to ensure they are working properly. Finally, the ballast could be the issue (more on that later).

Flickering. If the tubes are flickering, seating could also be at play. Make sure that the tubes are properly seated first and foremost. From there take a look to see if any of the tubes have burned out. You will see darkening at the ends in this case. If that doesn’t do it, check the starter. Finally, if the starter is not at fault, then the ballast will have to be replaced.

Humming or buzzing. If you notice a humming or buzzing, the ballast is typically at fault. Replace that and the humming or buzzing should dissipate.

What are the Signs of a Bad Ballast?

Since the ballast is one of the most common issues with lighting, it is important to know when yours may be going bad. Since the ballast is what distributes the current, it only makes sense that a malfunctioning ballast would cause issues with the fluorescent lighting. There are three common signs that the ballast is going bad.

  • No lights. Though it could be potentially indicative of other problems, no lights are a sure sign that something is wrong. After checking to see if the bulbs are still in good shape, the ballast is the next best place to check. In fact, it is possible that the ballast has burned out all of the tubes.
  • Buzzing. Contrary to what TV says, your fluorescent lighting should not be buzzing or humming. This is the most obvious sign that the ballast is going. What’s happening is that the ballast is having difficulty maintaining current, causing audible problems with voltage regulation.
  • Dimming or Flickering. When the bulbs take a while to get up to full brightness or even strobe, the reason is often the ballast. This is just another sign that the ballast is failing to properly regulate the current.

Check for Physical Signs on the Ballast

You could also opt to check the ballast itself. There are sometimes obvious indications that the ballast is either on its last legs or shot entirely. Before checking, make sure to turn off the power at the circuit breaker.

  • Water damage. There can be moisture either within the panel or on the interior of the ballast. Moisture is bad news and will fry your lighting.
  • Burn marks. You may have to crack open the ballast to see what’s inside. Should you notice burn marks either on the wires or the interior, replace the ballast entirely. The current got unmanageable and overloaded the ballast.
  • Swollen casing. Before you even get the casing off, you may notice the plastic on the ballast bulging. It means that the ballast was overloaded, and the box damaged along the way. Replace it entirely at this point.

Replacing the Ballast

In any fluorescent lighting system, the ballast is what regulates current into each of the lamps. It is also what provides the sufficient amount of voltage that is needed to start the lamps. When the ballast can’t limit the current, the fluorescent lamp that is directly connected to a high-voltage power source would experience a rapid increase in current draw.

  • Turn off power. Start by cutting off power to the circuit. Never mess around when it comes to electrical currents.
  • Remove the tube. Next, remove both the tube and the cover plate that hides all of the inner workings. Make sure to set them off to the side.
  • Wiring. The wires running to the tube holder or ballast need to either be disconnected or cut and then removed entirely. Have a proper set of wire cutters here. Next, strip off the ½” insulation at the very ends of the wiring.
  • Mount the new ballast. Take the new ballast and mount that component to the exposed wiring. Use wire nuts to adequately secure everything. Double-check to make sure that the wire nuts are secure the new ballast properly mounted.
  • Replace and check. Put the new ballast in place, replacing the cover and tube when you are finished. With everything back in place, turn the power to the circuit back on and give the switch a try. The fluorescent lighting system should work as normal again. If it doesn’t, it may be time to replace the entire unit.

Replacing the Light Starter

Of course, there is the chance that the starter could be bad. Keep in mind that most newer fluorescent fixtures come with built-in starters or none at all. Most of the older ones, however, have a very visible starter that is easy to change. The starter is a silvery, small cylinder plugged into one of the holders.

  • Shut off the power. Always start with cutting the power to the circuit. Safety first when it comes to electrical currents.
  • Take out the tube. Remove the tube where the starter is connected. Set the tube aside safely even if you plan on changing out the tube, too.
  • Remove the starter. Give the starter a turn; about a quarter turn clockwise should do the trick. Pull out the starter and discard it.
  • Plugin the new one. Take the new starter and plug it in the old one’s place. Give it the same turn, this time counterclockwise, to lock it into place.
  • Replace the tube and test it. When you are confident that the new starter is securely in place, replace the tube. Restore the power to that circuit and give the light a try. If the problem isn’t resolved, try moving on to the ballast instead.

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Replacing Fluorescent Tubes

Sometimes, the simplest explanation is the most likely. It is always worth checking whether or not the light tubes have burned out and stopped working. Just about any light fixture faces this extremely common issue from time to time.

The best way to determine if the tube is bad is to look at the ends of the tube. If you notice that one or both ends have darkened, it is safe to assume that they have burned out and will need replacing.

  • Remove the old tube. Take out one of the old tubes and take it with you to a hardware or home improvement store. This will help you to properly identify the replacement that you need. You will see a series of letters and numbers, typically start with T (for “tube”). The numbering after the T indicates the diameter. So, if you see T12, that indicates that the diameter is 12/8 inch. If you are measuring on your own, make sure to include the pins in your length.
  • Replace the old tubes. With new tubes in hand, you should be able to pop the old ones out and replace them with the new ones. This is not only the easiest fix there is, but the cheapest as well. Just make sure to bring the old tube with you when looking for a new one.
Ryan Womeldorf
Ryan Womeldorf

Ryan Womeldorf has more than a decade of experience writing. He loves to blog about construction, plumbing, and other home topics. Ryan also loves hockey and a lifelong Buffalo sports fan.

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