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I have a two-bulb F28T5 light fixture that went out and replacing the bulbs with new ones did not fix it. So I replaced the ballast with a new one. The lights come on but go out within a second or so. I cleaned the prongs that hold the light with alcohol and a Q-Tip but that didn't help.

I bent the prongs inward slightly and then the bulbs stayed lit for at least five minutes, long enough that no one noticed when they went back out. I tried rotating the bulbs in their sockets again but, as before, they only stay on for a second and go out.

The only thing I can think is that, perhaps, one of the bulb holders is bad or loose but, with it staying on as long as it did before, I wonder if there's something I'm not thinking of.

  • Are the lamps in a cold location? Fluorescent fixtures don't work well or at all when it's cold (depends on the exact ballast but some are rated only for 50 ºF and up). – Hank Mar 7 '16 at 1:33
  • @HenryJackson No. Room temperature. Please see my comment to Wolf about the ballast. – Rob Mar 7 '16 at 1:36
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If the lights actually light then apparently the lamps and wiring are good. I would suspect the ballast.

Is your ballast rated for T5 or T8 lamps?

The 'F' on the lamp is just the wattage rating.

I believe the two lamps are incompatible with the ballasts designed for them respectively. A lot of the T5 ballasts are listed as high output or HO. shop for ballasts and I think you will find they are lists for one or the other but not both.

You need the lamps that match your ballast.

Good luck!

  • I think the people who sent us the replacement ballast sent the wrong one or don't know what they're doing. I did find a local supplier of the bulbs for this and I'll buy some tomorrow to test. – Rob Mar 7 '16 at 2:46
  • The lamps must physically fit and the ballast must match the lamps. And the lampholders must not be defective. That's it. The bulb must light! @Rob Stop throwing parts at it and research. Seriously. Just crack the back off the fixture, find the ballast, and get the model number off the paper label. That is the ballast you actually possess. Google the model# and look at the data sheet (a 2-4 page PDF). It will list the types of bulb compatible with it. Keep in mind it could still be bad lampholders. – Harper Mar 7 '16 at 3:17
  • @WolfHarper I replaced the ballast as I've stated. I don't need to take it apart to read that as I have another in front of me. I'm not throwing parts at it. I'm told by two people that the bulbs we have should work with that ballast. I ask the question because I'm doubting those people. My comment to ArchonOSX was because I decided to follow what was on the ballast. He, too, asked about the F type which I clearly stated in my question. Coming here indicates I am researching because I believe I am being mislead by others. You are not telling me anything I don't already know or have done. – Rob Mar 7 '16 at 3:30
  • You are right, and I apologize for being testy. I speak of the datasheet because I've often found it helpful when the label wasn't. And, probably should've mentioned this, the piece of paper in the box is usually not the datasheet. I generally get them via a web search for the part#. – Harper Mar 7 '16 at 21:29
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Lampholders (tombstones) are the cheapest component in a fluorescent fixture. I would definitely go there next. Inspect them for arcing or scorching. Also make sure the "backstab" connections in the back of the lampholders are secure. I could see a lampholder failing as the lamp warmed up. Make sure you bent the bulb pins the right direction so it presses harder against the contacts, not weaker. Several outlets online sell a good variety, but they are probably pretty standard.

Also double-check that the ballast and bulbs are compatible, it is easy to make errors in that area.

  • I do have a concern about ballast mismatch. The ballast sent to me as a replacement does not list the bulbs that came with the unit. I went to a lighting store and found that the bulbs listed on the replacement ballast are not what you would find in most stores but that the voltage and current rating should handle my bulbs just fine. iow, it shows a F24 and F32 bulbs on the replacement ballast while mine is a F28. – Rob Mar 7 '16 at 1:39
  • Search the web for the datasheet for the ballast and make sure the whole number (F28T5) is listed. Electronic ballasts have enough smarts that I don't trust voltage and current parameters. – Harper Mar 7 '16 at 2:01
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When electronic ballast were mandated one big difference was the range of lamps they could support multiple or universal input voltage and more lamp types than the old mag ballasts. With that said it is import and your lamp type is listed on the ballast for example a straight t5 ho lamp with a non HO ballast will overheat and shutdown. Although t5 led retrofits are harder to find you may want to consider a lamp retrofit (get a quality DLC certified retro kit) I have hundreds of fixtures and have started replacing the Flouresents with LED ballast bypass then you won't have any more ballast problems. Note there are several advantages here. First is lower operation cost. 2nd Flouresents light level drop off quickly I just put a t5 led a few feet from a fixture that was relamped last year, the difference in light output is huge (same wavelenth or light color). Since you have a 2 bulb fixture you could change over for ~$20 and not have to worry about ballast compatibility. If you stay with Flouresents make sure the lamp type is listed.

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