# Fluorescent Bulb Only Half-Lights **URL:** \ **Category:** Factual Questions\ **Created:** [August 11, 2011, 12:46am UTC](https://boards.straightdope.com/t/fluorescent-bulb-only-half-lights/592276 "2011-08-11T00:46:11Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![Jinx](https://avatars.discourse-cdn.com/v4/letter/j/c6cbf5/32.png) [@Jinx](https://boards.straightdope.com/u/Jinx)\ **Post date:** [August 11, 2011, 12:46am UTC](https://boards.straightdope.com/t/fluorescent-bulb-only-half-lights/592276/1 "2011-08-11T00:46:11Z")
I am trying to replace a 12-in long fluorscent bulb with the diameter of a pretzel stick. It is used for a reading lamp built into a headboard. The replacement bulb will only half-light (at each end) although I am 99% sure it is seated as best as possible. I am afraid I will break the bulb if I try to turn it any further (to rotate the prong contacts at each end deeper into the lamp’s sockets). Any suggestions? FYI: The lamp says it takes a size T5 bulb, and I have a model F8T5 bulb. They look identical, so I assume this is the correct size, right? ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [August 11, 2011, 1:04am UTC](https://boards.straightdope.com/t/fluorescent-bulb-only-half-lights/592276/2 "2011-08-11T01:04:24Z")
I’m going to guess you have a bad starter or ballast though it’s possible the bulb you bought is bad as well, it’s been known to happen from time to time. ---
**Author:** ![Ostrya](https://avatars.discourse-cdn.com/v4/letter/o/35a633/32.png) [@Ostrya](https://boards.straightdope.com/u/Ostrya)\ **Post date:** [August 11, 2011, 1:04am UTC](https://boards.straightdope.com/t/fluorescent-bulb-only-half-lights/592276/3 "2011-08-11T01:04:53Z")
The F represents, length. Like the F96’s I have a box of are designed for a 96 in fixture, the tubes however are 93 in actual length, the rest of the length to make the 96 inches comes from the thickness of the end tabs the lamps mount into. I had read that years ago, not sure why it would say F8 - that would mean it was for an 8 inch fixture. So hopefully someone else will come along and I can be corrected. T represents increment of 1/8 in diameter, so a T5 would be 5/8 in diameter. I suspect it’s not seated correctly, seems the most logical problem if the ballast was working fine before when using old bulb. Btw, does the new bulb look just like the old bulb? ---
**Author:** ![Ostrya](https://avatars.discourse-cdn.com/v4/letter/o/35a633/32.png) [@Ostrya](https://boards.straightdope.com/u/Ostrya)\ **Post date:** [August 11, 2011, 1:08am UTC](https://boards.straightdope.com/t/fluorescent-bulb-only-half-lights/592276/4 "2011-08-11T01:08:48Z")
Joey P is probably right. Maybe ballast was the problem in the first place, and not the tube. Or tube is defective? Can anyone clarify on what the F8 means on the tube? ---
**Author:** ![Jinx](https://avatars.discourse-cdn.com/v4/letter/j/c6cbf5/32.png) [@Jinx](https://boards.straightdope.com/u/Jinx)\ **Post date:** [August 11, 2011, 1:16am UTC](https://boards.straightdope.com/t/fluorescent-bulb-only-half-lights/592276/5 "2011-08-11T01:16:13Z")
> [@the lone cashew](#): > > Btw, does the new bulb look just like the old bulb? Yes, it does look the same. ---
**Author:** ![Ostrya](https://avatars.discourse-cdn.com/v4/letter/o/35a633/32.png) [@Ostrya](https://boards.straightdope.com/u/Ostrya)\ **Post date:** [August 11, 2011, 1:17am UTC](https://boards.straightdope.com/t/fluorescent-bulb-only-half-lights/592276/6 "2011-08-11T01:17:51Z")
Sorry about that, saw you had already said that in your OP, was too late to edit my post. ---
**Author:** ![Jinx](https://avatars.discourse-cdn.com/v4/letter/j/c6cbf5/32.png) [@Jinx](https://boards.straightdope.com/u/Jinx)\ **Post date:** [August 11, 2011, 1:19am UTC](https://boards.straightdope.com/t/fluorescent-bulb-only-half-lights/592276/7 "2011-08-11T01:19:13Z")
How do you recognize what the ballast looks like? The end pieces that support the bulb look like one piece virtually contiguous with the lamp fixture…unless I am overlooking something? Also, don’t some fluorescent lamps not need a ballast, or am I confused with what (IIRC) is called a “starter”? ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [August 11, 2011, 1:23am UTC](https://boards.straightdope.com/t/fluorescent-bulb-only-half-lights/592276/8 "2011-08-11T01:23:04Z")
The ballast is inside the case. A starter looks like a round piece of metal about the size of a film canister sicking out of the case, usually behind the bulb somewhere. You would have one or the other. I’m not sure what something that small would have, probably some sort of mini electronic ballast. I’m not even sure if you could easily find a replacement ballast for it. If you have a starter\*, you could try replacing it, if it’s a ballast it’s usually easier to just replace the fixture. At work I replace ballasts, but only because 8 foot ceiling mounted fixtures are a bit unwieldy. I have a similar size light fixture in my basement, if I put a bulb in and it didn’t work, I’d probably just get a new fixture before I sunk any money into it. \*I’m thinking you have a similar light to mine, and I don’t think it would have a starter, I don’t even think it would fit in the case, in fact I don’t think fixtures made in the last 10 or 15 years even have them anymore. ---
**Author:** ![Ostrya](https://avatars.discourse-cdn.com/v4/letter/o/35a633/32.png) [@Ostrya](https://boards.straightdope.com/u/Ostrya)\ **Post date:** [August 11, 2011, 1:27am UTC](https://boards.straightdope.com/t/fluorescent-bulb-only-half-lights/592276/9 "2011-08-11T01:27:14Z")
As far as I know, all fluorescent lamps require a ballast. But the fixtures I have always worked with were all T12’s, so you need someone knowledgeable about your particular fixture, a T5. So I’ll just be be reading along on the sidelines. ---
**Author:** ![Jinx](https://avatars.discourse-cdn.com/v4/letter/j/c6cbf5/32.png) [@Jinx](https://boards.straightdope.com/u/Jinx)\ **Post date:** [August 11, 2011, 1:45am UTC](https://boards.straightdope.com/t/fluorescent-bulb-only-half-lights/592276/10 "2011-08-11T01:45:58Z")
> [@the lone cashew](#): > > The F represents, length. Like the F96’s I have a box of are designed for a 96 in fixture, the tubes however are 93 in actual length, the rest of the length to make the 96 inches comes from the thickness of the end tabs the lamps mount into. I had read that years ago, not sure why it would say F8 - that would mean it was for an 8 inch fixture. So hopefully someone else will come along and I can be corrected. > T represents increment of 1/8 in diameter, so a T5 would be 5/8 in diameter. > > I suspect it’s not seated correctly, seems the most logical problem if the ballast was working fine before when using old bulb. Btw, does the new bulb look just like the old bulb? My mistake… It is an 8-inch bulb. So, F8 means 8-inch length. ---
**Author:** ![Jinx](https://avatars.discourse-cdn.com/v4/letter/j/c6cbf5/32.png) [@Jinx](https://boards.straightdope.com/u/Jinx)\ **Post date:** [August 11, 2011, 1:49am UTC](https://boards.straightdope.com/t/fluorescent-bulb-only-half-lights/592276/11 "2011-08-11T01:49:18Z")
I do recall a slight struggle installing the original bulb, but it did light without incident. Now, this is the first replacement. I wonder if these tiny fluorescent fixtures are prone to having issues. Perhaps a more conventional fluorescent lamp (for a ceiling or even a desk lamp) is better built as I’ve rarely had an issue with any of them in a lifetime. ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [August 11, 2011, 1:51am UTC](https://boards.straightdope.com/t/fluorescent-bulb-only-half-lights/592276/12 "2011-08-11T01:51:59Z")
when you insert bulbs (lamp off or unplugged) they should rotate a full 90 degrees. place a mark on the bulb (on the circumference of the metal cap) midway between the pins helps you see when it is positioned correctly. turn by holding the metal end caps. ---
**Author:** ![Snnipe\_70E](https://avatars.discourse-cdn.com/v4/letter/s/b5a626/32.png) [@Snnipe\_70E](https://boards.straightdope.com/u/Snnipe_70E)\ **Post date:** [August 11, 2011, 2:57am UTC](https://boards.straightdope.com/t/fluorescent-bulb-only-half-lights/592276/13 "2011-08-11T02:57:11Z")
A lot of inexpensive light fixtures are built not to have the ballast changed. If you want to locate the ballast. Follow the wires from the sockets back to the insides of the fixture. Where they all meet will be the ballast. Few department stores (none that I know of) carry ballast for small T5 lights. And if you find one the ballst will cost more than a new fixture. ---
**Author:** ![Tim\_T-Bonham.net](https://avatars.discourse-cdn.com/v4/letter/t/46a35a/32.png) [@Tim\_T-Bonham.net](https://boards.straightdope.com/u/Tim_T-Bonham.net)\ **Post date:** [August 11, 2011, 7:22pm UTC](https://boards.straightdope.com/t/fluorescent-bulb-only-half-lights/592276/14 "2011-08-11T19:22:24Z")
> [@the lone cashew](#): > > I suspect it’s not seated correctly That seems unlikely. In most cases, if it’s not seated correctly, it won’t light at all. If it is seated enough to get a complete electrical circuit, it should work. Problem is likely to be somewhere else (like the ballast). ---
**Author:** ![Ostrya](https://avatars.discourse-cdn.com/v4/letter/o/35a633/32.png) [@Ostrya](https://boards.straightdope.com/u/Ostrya)\ **Post date:** [August 12, 2011, 2:35am UTC](https://boards.straightdope.com/t/fluorescent-bulb-only-half-lights/592276/15 "2011-08-12T02:35:11Z")
> [@t-bonham@scc.net](#): > > That seems unlikely. In most cases, if it’s not seated correctly, it won’t light at all. If it is seated enough to get a complete electrical circuit, it should work. Problem is likely to be somewhere else (like the ballast). I stand corrected, thanks for clarifying.