How to Fix a Fluorescent Light That Won’t Turn On

by Michael on December 30, 2010 · 0 comments

One of my projects for holiday break has been to fix the under-cabinet lighting in our kitchen. We have a series of fluorescent fixtures that use the skinny little T5 bulbs. Some have started flickering and flashing, while others just won’t turn on.


While it’s possible that the bulbs need to be replaced, that’s actually the least likely explanation when you start having trouble with fluorescent lights. A more likely (and cheaper) explanation is that the starters have worn out.

For those that are unaware, many fluorescent fixtures rely on a starter to light the lamp. The starter is a little cylinder that plugs into a socket in the fixture. The starter’s job is to send a pulse of electricity that lights the gas within the bulb.

To remove the starter – which is often metallic grey, though they can also be beige, white, etc. – you may need to first remove the bulb. Start by making sure the power is off, pop out the bulb, and then give the starter a gentle counter-clockwise twist to get it out.

Take a good look at the starter, and write down any information you see. The main thing you’re looking for is a code like FS-2, FS-4, FS-5, etc. Starters are sized based on the wattage of the bulb that they’re responsible for lighting, so make a note of the wattage, as well.

At the store, simply find a match to your old starter. Since the starter might have been mis-sized in the first place, you might also want to double-check the starter against the wattage of the bulb it’s responsible for lighting.

Our fixtures use a combination of 12 inch, 8 watt and 21 inch, 13 watt bulbs, so I picked up FS-5 and FS-2 starters (respectively). I also picked up some spare bulbs just in case I needed them.

If you replace both the starter and the bulb and it still doesn’t work, then you either have a power problem (maybe the switch is bad?) or the ballast is out. Replacing the ballast goes beyond the scope of this article, but it’s a fairly straightforward process.

As before, make sure you cut the power to the circuit that you’re working on. Next, disassemble the fixture and collect all of the relevant details from the old ballast. Now go buy a replacement and then rewire the new one exactly as the old one was hooked up.

Note that it is sometimes more costly to buy a ballast vs. replacing the entire fixture, so take that into consideration when you’re at the hardware store or electrical supply shop.

Obviously, if you’re not comfortable working with electricity, you should use your judgement when deciding whether to tackle something like this. The bulb and starter replacement are straightforward, but replacing the ballast is a bit more involved.


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