I have a fluorescent light fixture that's over 20 years old. Light failed so I bought two new 48" bulbs. Only one of the new bulbs light. New bulbs both work. There is no visible starter. Power must be getting to the unit, since one bulb lights up.

How do we fix this?

  • Can you get us photos of the ballast (big black rectangular lump) inside the fixture? – ThreePhaseEel Jan 18 at 2:14

Remove the metal cover from the fixture. There's a black ballast inside that is probably causing your problem. Take some pictures of the wiring and then disconnect all the wires going to the ballast, after turning off the power. Bring the ballast to a home store or electric supply store for a replacement. Then just re install it. A bit of friendly advise: just buy a new fixture as it will probably be cheaper than buying the ballast.

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    ...but (not from a home store) a replacement ballast might be better than the light fixture that's cheaper than it. And cheaper than the home store ballast. – Ecnerwal Jan 18 at 2:19
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    @JACK I usually agree with you, but some older fixtures are quite elegant and may match the "style period" of the house. A couple of years ago there was a florescent fixture in my mom & dad's house that was failing. One of my brothers tried replacing the tubes and that didn't work and gave up. So I took over and replaced the ballast with one that didn't need "starters" and it's working fine. It's a beautiful mid 1950s fixture that would have been a shame to toss. So even if a bit more expensive to repair, depending upon the design of the fixture, it may be worth saving. – George Anderson Jan 18 at 2:38
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    Thank you all for your responses. In fact, it is an ugly old fixture over my work bench, hung there by chains! I will check the cost of a new ballast as well as the cost of a new unit. – Paul Gottlieb Jan 18 at 3:16
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    Or ditch the ballast and use the new LED tubes that connect directly to the mains. Last time a ballast went in my house it was cheaper to buy the LED tubes than a new ballast, plus less electricity to power them. – Jon Custer Jan 18 at 15:50
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    @JonCuster Second benefit - LEDs work when it's freezing cold out. Fluorescents can take a while to slowly warm up and don't like to start when it gets really cold. For cold climate unheated workshops or garages it's a big win to switch to LED from fluorescent tubes and CFLs for that reason alone. – J... Jan 18 at 19:31

First, this sort of problem is often a broken lampholder ("tombstone"), or failing to get the bulb to seat correctly. The tubes have little "tick" marks molded into the metal end caps to help you see when the pins are square-on engaged.

However it is also possible for a ballast to be broken. Ballasts are pretty easy to replace, if you pick the correct replacement ballast so the wires just match up. For that, you'll need to take the bulbs out and look for an access cover to get to the ballast, remove that, and shoot us a pic of ballast and the 5-8 wires coming out of it. Sharp picture of the label wiring diagram will help too. (yes, I'm aware there won't be any light in the room lol).

A new ballast will be silent, start in the cold and never, ever flicker. That, with the new ~90 CRI bulbs you just bought, you won't believe it's the same light!

Once you're "in for a penny, in for a pound" with a ballast replacement, there are 2 possible upgrades to consider.

  • T8 real fluorescent, which uses T8 (1" diameter) tubes and a T8 ballast. They are about 25% more efficient, but use a different ballast that is incompatible with classic T12 (1-1/2" diameter) tubes. These tubes last a VERY long time.
  • LED replacement "tubes", which are even more efficient, but the wiring is weird and hard to explain. The light isn't quite as good as real fluorescent and the reliability is much worse than it ought to be. Just look at the ceiling of a big box store that has converted (and they're buying the good stuff, not the Chinese crud we consumers have access to).

If you're interested in either upgrade, just ask.

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