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Flickering fluorescent may just need to have its ballast replaced

QuestionI have a two-bulb fluorescent fixture in the basement that flickers when I turn on the light. The lights eventually stop flickering, but it is sure annoying in the meantime. Can you tell me what I need to do to fix the problem?

AnswerI just went through the motions with a two-lamp fixture in my office. My guess with your fixture is that the ballast is dying and needs to be replaced; however, let's look at few other possibilities.

One possibility that needs to be considered up front is whether or not your basement is heated. If the ambient room temperature is not high enough to evaporate some of the mercury in the tube, the lamp will flicker until the tube is heated enough for some of that mercury to vaporize and allow the tube to fully illuminate. Try heating the room prior to turning on the light to see if this helps.

If heating the room doesn't work, then troubleshoot the fixture. First check the ends of the fluorescent tubes. If either end appears to be very dark (discolored), the lamp is defective or is coming to the end of its life. It's time to change the tubes, and it's better to change both tubes in a two-lamp fixture, especially when one lamp depends on the other to work; i.e., if one tube dies, the other will not receive any power and will not light up.

If there aren't any dark ends, check to see if the lamps are seated correctly in their sockets. Work on a stepladder and position yourself dead center of the tubes (make sure the power is off). Gently grab the tube near each end with both hands and rotate the tube either forward or backward until you feel the pins at the ends of the tube snap firmly into the sockets. Turn the power on to see if this corrected the flickering light. Caution: it is very easy to short circuit one end of the tube against the body of the fixture while inserting the tube into the socket, possibly damaging the tube or the ballast. Be sure the light switch is off when you remove or insert fluorescent tubes.

If this doesn't solve the problem, then remove both tubes and check to see if any pins are bent. A bent pin may not seat correctly in the socket.

If the light continues to flicker after this troubleshooting, then the ballast or starter needs replacing. A flickering lamp can cause the ballast to overheat and fail prematurely and it can cause a starter to burn out.

Unless your fixture is around 20 years old, it probably does not have a starter. The starter, a little gray metallic cylinder that plugs into a socket attached to the fixture's frame, will be located under one of the tubes. You cannot troubleshoot a starter—simply replace it with a new one. To remove the starter, push in on it, turn it counterclockwise, and then pull it out. If you don't find a starter under one of the tubes, then you have a modern fixture that uses a ballast.

The ballast is attached to the fixture's frame with one screw. To find it, first turn off the power to the fixture, remove both tubes, and finally remove the electrical cover that snaps into place dead center full length of the fixture. Once it is removed, you can see all the color-coded wires that lead to the four sockets from the ballast. The ballast is normally black and has a wire diagram on its body.

There are many different ballasts (to handle different watts; different lengths of lamps; for 1-, 2-, and 4-lamp fixtures; and different sizes themselves) but only two main types: magnetic and electronic. I recommend that you bring your old ballast with you to the home center so you can match it with the correct one or match the ballast to tubes (watts) being used. Also, newer electronic ballasts are much more efficient and can save energy.

To remove the ballast—hold it securely with one hand while removing the screw located at one end because a ballast is heavy. Before removing it, I also recommend that you cut the wires coming from the ballast close to the unit so you won't have to drag a bunch of wires with you into the home center. Also, when you disconnect the power from the ballast, be sure to put wire nuts over the exposed wires in case someone turns on the power to the light.

When you install the new ballast, you'll have lots of wire to work with. I prefer to cut the existing wires about 6 inches away from the sockets and then use wire nuts to tie back into the new wires coming from the new ballast.

With a new ballast and new fluorescent tubes in your fixture, it will be like having a brand new light.

Copyright © 2005, 2006, & 2007 LAF/C.R.S., Inc. All rights reserved.
Question answered by Leon A. Frechette.

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C.R.S., Inc. · Spokane, Washington · USA

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