Fluorescent Lighting Repair and Use Q&A

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Dear NH,

I recently purchased a home with a walk-in closet. Since the small light in there was too dim, I had a repairman install a florescent light which is wired into the same wiring as the ceiling light. When the switch is turned on the ceiling light and the florescent light go on.

The problem is that the florescent fixture buzzes very loudly. Any idea how to eliminate the buzzing? Thanx.

MR from Pittston, PA


Not to my knowledge. Buzzing is characteristic "flaw" of fluorescent fixtures and is more pronounced in both inexpensive ones and old ones. The buzzing is often not noticed, especially during the day, because of other ambient noise.

I wish I had some encouraging news but unless one or our readers has a solution your choices are simple... either get used to it as a necessary annoyance OR replace it with one (or more) incandescent fixtures of higher wattage or even multiple recessed fixtures.

Dear NH,

I had a ballast fail on a florescent light fixture. After replacing the ballast, only one side comes on. The fixture has two horseshoe-shaped tubes. I wired the new ballast but only one tube light up. Yes, I've checked the bulb by switching it around and it does work. I was almost positive this was the way it was hooked up before but now I'm questioning myself. HELP!

RM from West Fargo, ND


Ballast installations are pretty straightforward, but with the number of wires you have to deal with they can be quite confusing... a two-tube ballast can have 10 wires! And, to make matters worse, sometimes the new ballast may have a different color configuration or number of wires than the original. Scary!

Had you consulted me prior to your adventure, I would have told you to make a detailed diagram of the wires and their colors... just in case... but it's too late for that now. So I will try to give you a little low-key fluorescent wiring theory to help you figure this problem out yourself.

First I will assume you purchased a compatible ballast by bringing the original with you to the hardware store. Also from your description, I gather your fixture has two bulbs so with that in mind...

There are two wires that connect to the electrical source... black and white. Black goes to the "hot" wire of your service and the white goes to the "neutral" wire. Since modern wiring conforms to this color scheme, the ballast connection is normally black-black and white-white.

One end of each fluorescent tube, regardless of the tube's shape, uses a common ground wire, which in your case would be yellow. Therefore, BOTH WIRES of the socket on ONE END of EACH BULB should be connected to the yellow wires.

The socket serving the other end of each tube would be connected to two wires, one socket going to the two red wires and the other socket connected to the two blue wires.

To reprise... one bulb has two yellow wires on one end and red wires on the other. The other bulb has yellow wires on one end and blue wires on the other.

Good luck... and next time LABEL THOSE WIRES!!

Dear NH,

My question is on wiring a florescent light fixture. I purchased six florescent shop lights which I intended to install in a new workshop I recently built. When I opened the shop lights I discovered that they had standard three prong plugs. Since I wanted to direct-wire these lights to come on with a wall switch I decided to cut the plug off. After cutting the plug off I discovered that there was no way to determine which wire is which except that the ground wire was green.

Does it matter which of the other two wires goes to the hot wire or can they be wired either way?


Yes, it does matter.  By switching the ground, hot, and neutral wires you may inadvertently produce an electrocution hazard in the metal frame of the fluorescent fixture. You will have to remove the cover on the fixture that hides the ballast and determine which wire in the cord is hot. Generally, the hot wire on the ballast is black, and the neutral is white. The other colors are the wires that connect the ballast to the fluorescent tube holders and to each other.

There is another issue, though.  These non-commercial fixtures are generally not UL-approved for hard wiring unless there is a manufacturer's fact sheet that says it's OK. So if there is no indication that hard wiring is approved, you will have to install new replacement three-prong plugs at the now cut ends of the power cords. These plugs are available at any hardware store.

To solve the ON-OFF problem, simply install an outlet box(es) near the fixtures, and wire the boxes so that it is controlled by a single wall switch!

Dear NH,

I have a couple of questions concerning fluorescent fixtures. First, how can you tell with a flickering or slow starting florescent light fixture whether to replace the lamp, replace the starter, or simply get a ladder and twist the tube? If the lamp has no starter but both tubes are misbehaving the same, is the problem both bulbs, the ballast (ouch!) or something else?

EN from Washington, D.C.

Generally speaking, a flickering fluorescent bulb means that one of the pair of bulbs in the fixture has bought the farm. My philosophy of sensible repair is to always replace both tubes. Fluorescent tubes have such a long life and are so inexpensive that it makes sense. Not that it's the most economical solution... it is just a practical viewpoint from someone who has been paid to do this type of work for others. To receive a second call in a month because the other of the two bulbs has gone bad is neither desirable from the customer's point of view ($$) or mine (pride in a job done right).

Fluorescent tubes can be tested with a multimeter by performing a continuity test across the pins on either end.  However, this is not a completely reliable test, since a loss of gas can also cause fluorescent failure. So for the handyperson, the best way to test the tubes is to install them in another fixture that you know functions. If you have a 4-tube fluorescent fixture, this is easy... remove one of the still-working pair of fluorescent tubes and replace it with each of the questionable tubes, one at a time. 99% of the time it will be one of the tubes that is the culprit.

However, if both tubes are functional, the problem is with the ballast or starter. The starter is replaced first, and if that does not solve the problem, the ballast should be replaced.

And a special note for the uninitiated... don't spend all day looking for a starter in your fixture! Most modern fluorescent fixtures do not have starters, so if it is not "in your face" (it looks like a small gray cylinder) your fixture don't have one. They are never hidden, though they may be concealed slightly by the tubes.

There is a good article on troubleshooting ballasts, using a multimeter here: http://www.doityourself.com/stry/how-to-troubleshoot-electronic-ballasts


Last newsletter, MR from Pittston, PA wrote about a problem he was having with a noisy fluorescent fixture. Some of our readers offered suggestions that are worth noting... and passing on...

GB suggested replacing the inexpensive magnetic ballast with an electronic ballast. However, he was wise to note that the replacement ballast might cost more than the fixture!! (In my research I found that electronic ballasts, besides being more expensive, are also more sensitive to heat than magnetic ballasts. Since some fixtures have the ballasts located right next to the bulbs, this heat MAY be an issue.)

KG offered two suggestions concerning possible problems with the wiring. First, if the fixture was as the end of a long run of wire, there might be a voltage drop that could cause a "dimming effect". Fluorescent fixtures are generally not dimmable... trying to do so can either cause them to go off OR produce some vibration in the ballast. KG also wondered if the installer properly grounded the fluorescent fixture. Old incandescent fixtures were typically not grounded, and lack of a ground could cause a ballast to become noisy!

CF and SR suggested checking that the ballast was securely mounted. Many ballasts vibrate to some degree, but a loose ballast will be even louder! CF suggested checking the entire fixture, not just the ballast. SR went a step further to suggest using a heat-resistant silicone caulk if tightening was futile.

There was wide consensus, though, that the cheaper the fixture, the noisier it will probably be! Thanks to all!