Humming light fixture

Humming light fixture · 11-01-2009, 03:46 PM

I hung some light fixtures this weekend. They are two-light four-foot T-8 fixtures, from Home Depot. In total, I have six lights (well, so far...). Four lights are on circuit A, two are on circuit B. Let's ignore the lights on circuit B.

To have some better control over the lights, I mounted two switches. Switch 1 controls lights A1 and A2, switch 2 controls A3 and A4 (the lights on B circuit also have a switch, but again, let's ignore these - they're fed by an entirely different panel).

Lights A1, A2 and A3 are perfectly quiet. Light A4 hums...but only if all four lights are on. If I switch A1/ A2 off, and only A3 an A4 are on), there is no hum. Any ideas what it could be? I could of course replace the humming fixture, but that may not fix it.

James Davis · 11-01-2009, 04:27 PM

Bas,

You might try listening to it for a moment and see if you can teach it the words so it don't have to hum anumore.

James

bobby g · 11-01-2009, 04:29 PM

Bas,

What else is on this circuit. Do these light fixtures have electronic ballasts? Can you measure the voltage at the fixture under the humming condition. Could be low line voltage caused.

Bob

JackLeg · 11-01-2009, 04:52 PM

I'm betting ballast!

Bas · 11-01-2009, 04:58 PM

Originally Posted by bobby g

Bas,

What else is on this circuit. Do these light fixtures have electronic ballasts? Can you measure the voltage at the fixture under the humming condition. Could be low line voltage caused.

Bob

There is nothing else on this circuit other than these 4 lights. I'll see if I can measure the voltage coming in, but I doubt it's anything other than 120.

Yes, they have electronic ballasts.

McRabbet · 11-01-2009, 05:11 PM

I would check to see that the ballast is tightly screwed/bolts to the fixture -- I've seen cases where that was the source of humming... If that is not the source, then I'd return the fixture for an exchange for a new one.

Ozzie-x · 11-02-2009, 12:13 AM

One of the good advantages of (good) electronic ballasts are that they are absolutely silent, which makes them great for schools, offices, libraries, etc. The first big T8 lamps/electronic ballast project I designed was a large multi-floor college library. When the project was finished, I did my final construction review and it was amazing. You could walk into one of the open stack floors (no furniture yet) that had maybe 200-300 2x4 light fixtures with (4) T8 lamps with electronic ballasts, and it was absolutely silent, no buzzing, no humming (or singing), you could literally hear a pin drop. A far cry better all the way around over the old magnetic ballasts, not to mention the 40% energy savings.

Sounds like some you have some kind of strange voltage drop problem. My money is on the ballast. Now this may not be it, but the Borgs all negotiate lower quality in the light fixtures with the manufacturers so the Borgs can buy the light fixtures cheaper from the mfgr and consequently sell them cheaper to the public. One of the things they do on flour. fixtures is to substitute crappy cheap off-brand ballasts. These ballasts typically have low ballast factors, low power factors, and other crappy electrical characteristics. This will cause increased energy usage, lowered light output, shortened lamp life, plus other safety concerns like overheating. (Make sure you mount the fixtures with the 1 1/2" air gap from any combustible material as required by the NEC). NEVER buy any of those $10 shop lights, they have the crappiest ballasts available that have a ballast factor less than 0.8, and that's why they look so dim, the cheap ballasts won't drive the lamps to full output, the lamps are probably running at less than 80% light output on day one, and it's downhill from there...

We've had 2 near fires here in the house from the junky chinese made light fixtures from Lowes, and I'm in the process of replacing them with brand name quality UL listed light fixtures from the electric supply house. I'll never buy another light fixture from the borgs. We all like to save money, but in lighting and so many other things, you get what you pay for, no free lunch, and all the other clichés. OK, rant mode off....

Phil S · 11-02-2009, 08:20 AM

Bas, Most likely the fixture and replacing it should eliminate the problem for now, but I bet the hum will be back but maybe not in that fixture. I would just take them all back and come over to my place and get four fixtures that have quality commercial ballast, or if you do not want to take them all down then just remove all the ballast and I will give you new ballast only. Either way your cost will be only something cold and carbonated. Phil

Bas · 11-02-2009, 09:50 AM

Originally Posted by McRabbet

I would check to see that the ballast is tightly screwed/bolts to the fixture -- I've seen cases where that was the source of humming... If that is not the source, then I'd return the fixture for an exchange for a new one.

I'll check that, certainly worth the 30 seconds.

Originally Posted by Ozzie-x

Sounds like some you have some kind of strange voltage drop problem. My money is on the ballast.

I'm sure it's the ballast. But I still wonder why it only hums when I have four lights on vs. just two. This is a brand new circuit that's < 50ft. wired with 12 gauge, and all I have on the circuit are 4 lights. But, I suppose it's possible that the ballast is so bad that even the slightest load causes it to dip below "working normally".

Originally Posted by Phil S

Bas, Most likely the fixture and replacing it should eliminate the problem for now, but I bet the hum will be back but maybe not in that fixture. I would just take them all back and come over to my place and get four fixtures that have quality commercial ballast, or if you do not want to take them all down then just remove all the ballast and I will give you new ballast only. Either way your cost will be only something cold and carbonated. Phil

Thanks Phil, I might just take you up on that. I'm not jumping up and down with the idea of taking the fixtures down and putting the new ones up (I hate working above my head...), but you gotta do what you gotta do. Either now or in the future. As for cold & carbonated stuff, that's _always_ available, fixtures or no

For the record - these are the T8 Lithonia fixtures from HD. I had good luck with them in my old shop. They ran fine for two years without a hum, and not a single bulb went out. But, I only had three of them, so that could have been dumb luck of course.'

Thanks for the feedback everyone.

Mt. Gomer · 11-02-2009, 04:55 PM

Originally Posted by Phil S

Bas, Most likely the fixture and replacing it should eliminate the problem for now, but I bet the hum will be back but maybe not in that fixture. I would just take them all back and come over to my place and get four fixtures that have quality commercial ballast, or if you do not want to take them all down then just remove all the ballast and I will give you new ballast only. Either way your cost will be only something cold and carbonated. Phil

Phil, I've got a few dim spots left in my shop that need to be remedied. If you need to get rid of some fixtures I'm happy to get in line behind BAS. I can bring plenty of Diet Coke....

Trav

TN Woodie · 11-03-2009, 07:55 AM

If you want to verify the bad ballast, swap two of them in the shop and see if the noise moves. If it does, you have nailed down the problem, if not, then it probably wasn't the ballast.

The problem with swapping out a new ballast is the possibility of getting another bad one, or the fixture is somehow the problem and it a new ballast doesn't fix anything.