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What is the buzzing sound in the lights when I dim them down?


What’s that buzz?

What’s that buzzing sound coming out of my light bulb?

Or - My fan buzzes when I turn the speed to low.

A number of our customers have made the following comment regarding a buzzing sound coming out of their light bulbs and other electrical items.

They seem to notice this problem just after a dimmer switch has been installed on a circuit containing incandescent or halogen light globes.

“We have dimmers on many of the lights in our house.  When the light is dimmed, a small buzzing sound can be heard coming from the light bulb. It can be quite irritating. The sound doesn’t seem to come from the dimmer switch itself but from the light bulb.  Why does the dimmer switch make the light bulb buzz?”

From John S. Hillcrest 92103

Sometimes you can get a buzzing sound coming out of the dimmer switch to, as a nice lady named Gertrude from Mission Hills 92103 informed us on a service call we recently did for her.

Also, we have encountered buzzing coming from fan speed control knobs.

Customers have asked why these things buzz like they do?


The exact reason for the buzzing is a bit complicated to explain, but I will go through the basics here.

The first thing to understand is that the lights and fans in your home are typically powered by AC voltage. The AC voltage sine wave is normally smooth and interacts magnetically in a smooth way with the light or fan that it is powering, thus quiet operation of the internal parts.

If you want to dim a light or control the speed of a ceiling fan, the dimmer switch or fan speed control will modify the AC voltage sine wave to the light or fan. The voltage to your light or fan is typically mollified by clipping the AC voltage sine wave using the dimmer switch or fan speed control to do this job.

When the AC voltage sine wave is clipped, it makes sharp spikes and drops on the smooth waveform causing magnetic interference with the internal components of your light or fan.

This magnetic interference causes the internal parts to vibrate at the rate of the incoming clipped AC power sine wave. Thus you can hear a buzzing sound coming from the internal parts.

That is the answer for why things buzz, but is there anything that can be done about it?

There is no simple answer to solving this problem. 

You can try a few things before calling an electrician to deeply analyze your problem.

1) Make sure your dimmer switch is not under rated for the amount of lighting wattage you have put on it.

2) For best results, a dimmer switch should have maximum loading of about 75% or 60% for coolest and operation.  Also, look for dimmer switches that have internal filters for smoothing out the AC power sign wave.

3) Fan speed controls are a more difficult problem to solve as the fan speed controller should be matched to the type of motor used in the fan.  The quietest ceiling fan controllers we know of are the capacitive types that are pre-built into the fan body and controlled by the pull chain. There are some remote units that work like this too.

For deeper detail on exactly how and why this works, check out the webpage below.