# Fluorescent fixture not working right **URL:** \ **Category:** Factual Questions\ **Created:** [July 15, 2005, 7:34pm UTC](https://boards.straightdope.com/t/fluorescent-fixture-not-working-right/312701 "2005-07-15T19:34:10Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![Joe\_Mahma](https://avatars.discourse-cdn.com/v4/letter/j/5daacb/32.png) [@Joe\_Mahma](https://boards.straightdope.com/u/Joe_Mahma)\ **Post date:** [July 15, 2005, 7:34pm UTC](https://boards.straightdope.com/t/fluorescent-fixture-not-working-right/312701/1 "2005-07-15T19:34:10Z")
The fluorescent fixture (2 42" bulbs) has begun to light at about 20% of normal brightness (maybe less- it’s hard to estimate). Is ther an easy way to tell if the problem is bulbs or ballast? ---
**Author:** ![racer72](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/racer72/32/3075_2.png) [@racer72](https://boards.straightdope.com/u/racer72)\ **Post date:** [July 15, 2005, 7:44pm UTC](https://boards.straightdope.com/t/fluorescent-fixture-not-working-right/312701/2 "2005-07-15T19:44:20Z")
It appears the ballast is failing. The only way to tell is install a couple new light bulbs and make sure they are fully seated. If the bulbs are failing you will see distinctive black mark inside the tube at each end caused by the excessive heat from the cathode trying to keep the bulb lit. I change quite a few fluorescent bulbs and light fixtures as part of my job, we have the luxury of just removing the possibly bad lights and bulbs and installing new ones, we don’t spend much time troubleshooting the cause of the light failure. ---
**Author:** ![Joe\_Mahma](https://avatars.discourse-cdn.com/v4/letter/j/5daacb/32.png) [@Joe\_Mahma](https://boards.straightdope.com/u/Joe_Mahma)\ **Post date:** [July 16, 2005, 1:01pm UTC](https://boards.straightdope.com/t/fluorescent-fixture-not-working-right/312701/3 "2005-07-16T13:01:40Z")
> [@racer72](#): > > It appears the ballast is failing. The only way to tell is install a couple new light bulbs and make sure they are fully seated. If the bulbs are failing you will see distinctive black mark inside the tube at each end caused by the excessive heat from the cathode trying to keep the bulb lit. I change quite a few fluorescent bulbs and light fixtures as part of my job, we have the luxury of just removing the possibly bad lights and bulbs and installing new ones, we don’t spend much time troubleshooting the cause of the light failure. Thanks, **racer**. I was hoping to avoid a bulb swap (Home Depot said they won’t take 'em back), but if that’s the only way, I’ll give it a try. ---
**Author:** ![Uncommon\_Sense](https://avatars.discourse-cdn.com/v4/letter/u/f9ae1b/32.png) [@Uncommon\_Sense](https://boards.straightdope.com/u/Uncommon_Sense)\ **Post date:** [July 16, 2005, 1:52pm UTC](https://boards.straightdope.com/t/fluorescent-fixture-not-working-right/312701/4 "2005-07-16T13:52:33Z")
I repair several flourescent fixtures each week (I maintain a facility with several thousand of them). The most common reason for poor light output is the tube itself (bulb, lamp, etc, all the same). You should always start with replacing the tubes first. The ballast are more costly (they sometimes cost more than the fixture). One way to tell if the ballast is shot is by touching the part of the fixture that contains the ballast or the ballast itself, if it is cold, then the ballast is shot. In your case, the lights are sort of working (in my experience if the lights are putting out ANY light at all then it’s the tubes that need to be replaced) so you have a good idea that it’s the tubes. In your case, if one tube goes out then it’s the tube that’s bad, not the ballast. If both tubes are dim then it’s one tube or the other or both. If both tubes are out then it could one tube or the other or both or the ballast. Another possibility, though not in your case, is you could have a loose wire in the end socket(s) or a bad socket which might be cracked, burned, etc. Start with replacing the tubes, you should get normal output again. Always replace tubes in pairs. IOW, replace both if you replace one. Tubes are designed to last about 20,000 hours (average, some last 3 days and some last 30 years). Ballasts can last anywhere from ten to twenty years with average use. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [July 17, 2005, 4:22pm UTC](https://boards.straightdope.com/t/fluorescent-fixture-not-working-right/312701/5 "2005-07-17T16:22:49Z")
> [@Uncommon Sense](#): > > Another possibility, though not in your case, is you could have a loose wire in the end socket(s) or a bad socket which might be cracked, burned, etc. This is probably not the problem, but it should also be mentioned that (for most fixtures) the metal reflector must be connected to ground. ---
**Author:** ![spingears](https://avatars.discourse-cdn.com/v4/letter/s/ebca7d/32.png) [@spingears](https://boards.straightdope.com/u/spingears)\ **Post date:** [July 18, 2005, 2:28am UTC](https://boards.straightdope.com/t/fluorescent-fixture-not-working-right/312701/6 "2005-07-18T02:28:59Z")
> [@Crafter\_Man](#): > > This is probably not the problem, but it should also be mentioned that (for most fixtures) the metal reflector must be connected to ground. Also newer fixtures require that the metal cover must be in place over the ballast for the fixture to work properly. ---
**Author:** ![Uncommon\_Sense](https://avatars.discourse-cdn.com/v4/letter/u/f9ae1b/32.png) [@Uncommon\_Sense](https://boards.straightdope.com/u/Uncommon_Sense)\ **Post date:** [July 18, 2005, 2:50am UTC](https://boards.straightdope.com/t/fluorescent-fixture-not-working-right/312701/7 "2005-07-18T02:50:58Z")
> [@spingears](#): > > Also newer fixtures require that the metal cover must be in place over the ballast for the fixture to work properly. More precisely, the lengths of the tubes must be at least a certain distance away from the grounded metal part of the fixture for the tubes to work efficiently or in some cases to work at all. ---
**Author:** ![Joe\_Mahma](https://avatars.discourse-cdn.com/v4/letter/j/5daacb/32.png) [@Joe\_Mahma](https://boards.straightdope.com/u/Joe_Mahma)\ **Post date:** [August 8, 2005, 10:13am UTC](https://boards.straightdope.com/t/fluorescent-fixture-not-working-right/312701/8 "2005-08-08T10:13:09Z")
After 2 months of low light output, things suddenly went back to normal yesterday. ??? I’m thinking this implicates the ballast, as I don’t think the bulbs could return to normal if they were toasted. ---
**Author:** ![spingears](https://avatars.discourse-cdn.com/v4/letter/s/ebca7d/32.png) [@spingears](https://boards.straightdope.com/u/spingears)\ **Post date:** [August 9, 2005, 12:50pm UTC](https://boards.straightdope.com/t/fluorescent-fixture-not-working-right/312701/9 "2005-08-09T12:50:30Z")
> [@Joe Mahma](#): > > After 2 months of low light output, things suddenly went back to normal yesterday. ??? I’m thinking this implicates the ballast, as I don’t think the bulbs could return to normal if they were toasted. **The first trick to try** is to rotate the tube(s) slightly to insure that the end pins are making good contact in the sockets. ---
**Author:** ![Kalhoun](https://avatars.discourse-cdn.com/v4/letter/k/3bc359/32.png) [@Kalhoun](https://boards.straightdope.com/u/Kalhoun)\ **Post date:** [August 9, 2005, 1:09pm UTC](https://boards.straightdope.com/t/fluorescent-fixture-not-working-right/312701/10 "2005-08-09T13:09:15Z")
Just as a sidebar… We have flourescent bulbs in our kitchen ceiling fixture. This light is on 24/7. And it lasts for a full decade at a time! How can that be??? ---
**Author:** ![bigdog0629](https://avatars.discourse-cdn.com/v4/letter/b/d78d45/32.png) [@bigdog0629](https://boards.straightdope.com/u/bigdog0629)\ **Post date:** [December 11, 2012, 9:02pm UTC](https://boards.straightdope.com/t/fluorescent-fixture-not-working-right/312701/11 "2012-12-11T21:02:42Z")
Hello, I installed nine flourescent lights for a sign company. Two of the lights in the series would not work. I ensured that power was coming in and the bulbs are brand new. I did notice when I went to put the second bulb into the socket it shocked me. Would this be some type of grounding issue? Right as I was putting the second one in the first one flickered on, but went off when I set the second into place. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [December 11, 2012, 11:08pm UTC](https://boards.straightdope.com/t/fluorescent-fixture-not-working-right/312701/12 "2012-12-11T23:08:28Z")
> [@bigdog0629](#): > > I did notice when I went to put the second bulb into the socket it shocked me. Would be hard to believe the bulb shocked you, since its envelope is made of glass. Are you saying you received a shock when you touched the fixture’s metal housing or reflector?