View Full Version : flourescent lights won't work together

08-12-2009, 11:45 AM
I'm having a weird problem with the flourescent lights in my garage. The garage has 3 light fixtures, each with 2 long flourescent bulbs. They are controlled by a single switch. However, when I flip the switch, they will not all come on. Instead, they seem to randomly choose among themselves which fixture will light. Often, one fixture will light fully, another fixture will also light, but dimly, and the third won't light at all. But like I said, these functions seem to ramdomly occur among the 3 fixtures. Since I most need the light above the workbench, I just keep flipping the switch on and off 10-20 times until the right combination occurs that lights the workbench light fully.

Any ideas on why this is happening and what I can do to fix it?

08-12-2009, 11:58 AM
Ballast could be shot, if they have starters, those may need to be replaced, the bulbs may be old, it could be cold (florescents don't generally like cold), or you could have a wiring problem...something in series verses parallel, loose neutral or hot. Flakey switch. You may have the wrong lamps in there.

08-12-2009, 06:03 PM
these functions seem to ramdomly occur among the 3 fixtures
Fixtures and ballasts need to be grounded.


08-12-2009, 06:06 PM
check your connections

08-12-2009, 08:22 PM
Ground is an issue with this kind of fixture. A loose ground somewhere could be making all act up.

08-12-2009, 08:48 PM
Without a ground the bulbs can have difficulty establishing an arc. Check that the fixtures are properly grounded.

08-13-2009, 06:53 AM
I've had trouble with the electronic ballasts which are in those cheap lights you get at discount stores.

The solution is to replace the electronic ballasts with the old fashioned heavy metal ballasts. Then end of trouble!

Also be sure your 3 light fixtures are wired in "parallel".


08-13-2009, 06:56 AM
P.S. When I say parallel, I mean the main power wires to each fixture wired in parallel with each other. (Don't go messing with the internal wiring of the fixtures unless replacing the ballasts.)

08-13-2009, 08:59 AM
I don't think they make electronic ballasts for 8' tubes, (do they?)

Electronic ballasts are far more efficient than heavy iron, but bottom-of-the-line fixtures come with bottom-of-the-line ballasts too, some of which have operating temperature issues (both at high & low temp) as well as line noise susceptibility issues, etc. (Most are pretty good these days, but there was some real junk out there 8-10 years ago.)

If these are old-skool T12 (1.5" diameter) 4 or 8 footers with magnetic ballasts, the ground connections are critical, and it less-conditioned spaces like shops corrosion is common, so re-making all ground connections could fix the problem.

If these are 8 footers and ballasts are shot, replacing them with two 4-foot higher efficiency (with better color rendering!) T8 (1" diameter) fixtures can run about the same cost as a replacement ballast for the antique. The electronic ballasts all run at high frequency and are "flicker free", and the combined tube/ballast system produces ~90 lumens/watt instead of ~50 lumens/watt for an old magnetic-ballasted T12. T8s run cooler, look better, last longer, tubes are cheaper & more available, and they are cheaper to run. Cash invested in keeping T12 antiques going is usually money wasted.

If re-making all the connections to the fixtures doesn't make the problem go away and you're sure the wiring is good, move on (the world has.) IIRC, in CA under Title 24 it's even illegal to install magnetic ballasts now, since the systems can't meet the luminaire efficiency minimums.

Instant-start electronic ballasts are a bit hard on tubes, but run at higher efficiency. If this is somewhere the lights get turned on/off many times in a day it'll burn out the tubes quicker. Programmed-start versions may have a hesitation and start up at a slightly dimmed level ramping up to full-bright with 10-40 seconds, but they're ever so slightly lower efficiency (since they run a filament current in background, whereas the instant-starts don't.) In most applications the type of ballast-startup isn't very critical (as I expect it isn't in this case.)

08-13-2009, 06:34 PM
Your description implies that the lights are connected in series, and only one at a time gets enough voltage to operate.

08-13-2009, 07:29 PM
I don't think they make electronic ballasts for 8' tubes, (do they?)


Au contraire: http://advancetransformer.com/eCatalog/out/6083458841.pdf

08-14-2009, 07:39 AM
Thanks for all the suggestions. You've all given me some points to check. The lights in question are probably about 20 years old. I've lived in the house for 5 years, and they've had this problem as long as I've been here. I'll take a look at them based on the suggestions and see what I find.

08-14-2009, 10:57 AM
Au contraire: http://advancetransformer.com/eCatalog/out/6083458841.pdf


Note that this ballast is for a T8 tube, not a T12.

Finding the tubes in onesies twosies might take a bit of searching- certainly not a stock item at big blue or big orange box stores, but you can get 'em at Grainger.

Looks like Philips/Advance also makes electronic ballasts for 8' T12s as well:


I guess it's been awhile since I looked for one- they weren't available to me locally 6-7 years ago when I needed one in a hurry. I guess that where there's a large enough installed base, there's a market to support.

Thanks for the update!