Humming Vibration Noise from Fixture

grandmumOctober 2, 2012

I have a bathroom light fixture that holds 8x40w g12 incandescent. Recently a noticed a very faint, intermittent humming/vibration noise. I can make it start and stop by tapping on the fixture.

There is no flickering or dimming of the light. I removed all the bulbs and I could not get it to make the same noise without any bulbs in it (rule out house wiring??).

I isolated it to one of the bulbs by reinstalling each seperately. I tired a new bulb in that socket and it still occured and I could toggle the sound again from tapping on the metal surrounding of the socket.

Do you think its safe to say its just a normal vibration sound from a quirky socket?

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I apologize, tried to edit to add.... I can make the vibration/toggle occur by knocking on the wall... I know it sounds nuts but I ask so I dont waste money replacing the entire fixture.... thank you.

    Bookmark   October 2, 2012 at 1:23PM
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Upon further investigation, I cannot pinpoint it to any one socket/bulb. However, if I remove the bulbs there is no faint humming. It only occurs randomly with bulbs in the on position.

Im guessing its the filaments vibrating. However, I was under the assumption filaments would only "buzz" or "hum" when subjected to a dimmer. This is not the case.

So I guess my question is, do incandescent filaments/bulbs vibrate or hum under normal operation and would this be considered normal?

(again I hope I am not coming off like a nutcase)

    Bookmark   October 2, 2012 at 5:42PM
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Not surprising. The filament is subjected to 60HZ alternating current. The filament is a small coil, not a straight wire. That coil creates a small magnetic field that changes direction 60 times a second. So the filament may shake. Normally, the filament would be supported so that it would not shake. But it depends on the bulb.

    Bookmark   October 3, 2012 at 3:09PM
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My hearing is so bad that it would not be a problem. So while it is annoying to you, it points to your good fortune at having good hearing.

    Bookmark   October 4, 2012 at 8:45AM
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Thank you, my hearing is still ok.

I would definetly describe it as 60 cycle hum.

However, I am still confused why I can make it start and stop by banging on the wall next to the fixture? And why it wouldnt be there without bulbs in the fixture?
BTW: I replaced the G25 bulbs and even with new Sylvanias I am noticing the same situation.

    Bookmark   October 4, 2012 at 9:34AM
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Because it's coming from the bulbs themselves? Banging the wall shakes the filament around so the sound stops or starts.

    Bookmark   October 4, 2012 at 2:27PM
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Thanks for your patience. I apreciate your time in responding.

Do you think the intermittent nature of this constitutes removing the fixture for further investigation or should I not worry about it?

Im guessing its ok since its a subtle noise (not loud crackling or something) and there is no flickering of the lights (thinking if it was a loose connection banging on the wall and fixture would have made it flicker or dim.)

Thanks in advance from a Grandma with no Grandpa to check things like this out.

    Bookmark   October 4, 2012 at 8:04PM
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It appears the sound is most likely emanating from the filament coils of the 8 bulbs and not an electrical issue. It may just be reverberating due to loose mounting hardware.

If you can place your hand on the fixture and stop it, check to make sure the fixture is tightly secured to the electrical box. This would require opening the fixture to access the mounting screws.

It also sounds like this is some type of long bar fixture, so it may be the light bar vibrating against the wall. You may be able to dampen it with some foam tape underneath it at the far ends of the fixture or screws and plastic wall anchors.

    Bookmark   October 4, 2012 at 8:47PM
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Thanks Yosemitebill! You are right its an 8 G25 bulb vanity bar fixture. It has 1 screw on each side onthe bottom and what looks to be maybe a smaller than usual punchout on one side.

Do you think a loose connection/arc would sound more like I describe in this case?

This being an intermittent 60 cycle hum consistent in intensity but only noticeable if you listen real closely or more prounced if you put your ear to the drywall close by?

Judging by a loose connection at an arcing switch I had once, I would describe that as a more crackling louder noise, no strainging needed to hear that.

I apologize if I went on to long, you pro's probably think grandmum is off her rocker by now!!

    Bookmark   October 4, 2012 at 9:50PM
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If your still with me and havent abandonded a crazy old loon like myself...

Whats frustrating is that I believe this is something that just started (unless I just never noticed it before).

Also the fact its intemittent has me confused... it hasnt occured over the last 12 hours that I have noticed and I would either have to wait for it to mysteriously appear (perhaps closing the door or cabinet hard will get it singing) or I would have to bang around on the wall or fixture manually to make it occur.

    Bookmark   October 5, 2012 at 8:27AM
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Any bulbs replaced lately?

It could also be a bulb getting ready to fail.

More and more of the tungsten boils of the filament and moves to the inside of the glass globe (you may have seen clear bulbs with the dark 'tint' appearing on the inside of the glass).

Eventually a thin enough spot develops and the bulb 'blows' when turned on as it tries to heat up (the inrush current before the filament gets hot can be more than 50% higher tan the 'running' current).

    Bookmark   October 6, 2012 at 1:51PM
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thanks for the reply brickeye, when I first noticed it I swapped out the bulbs with new Slyvania g25 40's and it still intermittantly occurs.

Old grandmum is still perplexed, even a gentle knock on the wall next to the fixture causes it to start and stop.

    Bookmark   October 6, 2012 at 2:19PM
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" even a gentle knock on the wall next to the fixture causes it to start and stop.


Cheap bulbs or loose fixture mounting screws.

Not just the screws you may be able to see, but any screws concealed behind the fixture holding mounting brackets to the wall or the junction box behind the fixture.

Try just gently pushing on the fixture between the bulbs forsing it tighter to the wall.

Sometimes just touching it (even pushing on it or squeezing firmly with your hand) can dampen out the vibration.

Remember the bulbs will be flesh burning hot (and any metal near them).

    Bookmark   October 7, 2012 at 9:44AM
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