Ask MAKE: Why do lights buzz?

Ask MAKE is a weekly column where we answer reader questions, like yours. Write them in to becky@makezine.com or drop us a line on Twitter. We can’t wait to tackle your conundrums!

Martin writes in:

Why do my incandescent light bulbs buzz when I’m using a dimmer switch? What can I do to stop it?

Household lights run on alternating current (AC), which can be seen as a sine wave on an oscilloscope. To decrease the brightness of the bulb, a dimmer switch takes chunks out of the sine wave. This essentially turns the bulb on and off around 120 times every second, depending on the dimmer swtting. Charging the bulb filament creates an electromagnetic field, and when this field is turned on and off so rapidly, the changing force can cause the filament to start vibrating in sync with the frequency of the ons and offs.

To stop the buzzing, you can try rough service light bulbs, which have the filament anchored in more than two places, unlike regular light bulbs. Think of the filament supports as legs on a table. Two legs would make for a wobbly table, but make that three or four legs, and you’ve got something more sturdy.

If it’s your dimmer that buzzes instead of your light bulbs, you may need a dimmer rated for a higher capacity. Try removing some of the light bulbs connected to the dimmer and see if it makes a difference. If the buzzing is quieter, you may need a stronger dimmer. Common triac-based dimmers are controlling the chopping up of that AC wave, and can also vibrate because of it. Some higher quality dimmers have filters in them to prevent that.

Some more reading on the subject:

How to stop lighting dimmer switches from buzzing on Ask MetaFilter
Buzzing lights on Smarthome
Switches and Dimmers Buying Guide

Have you had to fix a noisy light problem in your house? Share with us in the comments.

This week’s Ask MAKE has been sponsored by Jameco Electronics.

8 Responses to Ask MAKE: Why do lights buzz?

Jaime on August 20th, 2009 at 9:56 pm said:

the charguer of my cellphone also sound ?
how did i stop it?

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Tom on August 21st, 2009 at 2:19 am said:

Interesting… before they were removed from supermarket shelves in favour of CFL bulbs, all the incandescent bulbs I ever saw for sale here had at least 4 support points.

I wonder why bulb manufacturers think Australia is that rough?

Jamie, I assume you are not running your cell phone charger via a dimmer switch, but it’s basically the same thing. A magnetic field is shaking a component, most likely the switchmode inductor or transformer. It can likely be fixed with an appropriately placed dab of epoxy or silicone rubber.

However switchmode power supplies are sometimes capable of storing a lethal amount of energy – even when unplugged. So if you don’t know what you are doing, get some help from someone who does.

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- anachrocomputer on August 21st, 2009 at 5:10 am said:
  
  Remember that Australia, like Europe, is a 220V country and the original poster was most likely in the U.S. (he mentions 60Hz mains frequency). So a 220V bulb filament may well be twice as long as a 110V bulb filament. And a longer filament may need more support along its length. Bulb filaments here in England usually have two supports in addition to the two end connections.
  
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  Becky Stern on August 21st, 2009 at 8:31 am said:
  
  Yep, thanks for pointing that out, I was referring to North America’s 110V AC power. Maybe one of the solutions to the buzzing problem is to move to Australia!
  
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  Simon on August 21st, 2009 at 11:12 am said:
  
  Moving to Aussie to get away from buzzing won’t work. Haven’t you seen the funny hats they wear for the flies
  
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SLE on August 25th, 2009 at 12:54 pm said:

So, my neighbor has an outdoor light that buzzes so loud it makes me want to punch myself in the ears, but since he’s older and his windows are double pained he thinks I’m full of crap. The light takes a while to “warm up” and get to full brightness, but once it does, the noise it makes is louder than anything I’ve heard from a light.

Any ideas on what I could do to help my neighbor fix his faulty light?

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- Matt Mets on August 25th, 2009 at 9:25 pm said:
  
  Based on the fact that it takes a few minutes to warm up, I would guess that the lamp is some sort of gas discharge lamp, such as Sodium-vapor (http://en.wikipedia.org/wiki/Sodium-vapor_lamp). Unfortunately, the buzzing in this kind of lamp is probably caused by a faulty ballast, so the ballast will probably need to be replaced.
  
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snarkyFish on September 3rd, 2009 at 9:52 am said:

It might be nice to have another one of these that explains why fluorescent lights / ballasts hum and buzz as well. I imagine it’s a very similar explanation, but a much more complicated fix.

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