What Causes Humming Light Bulbs?

jholmes · Joined: 23 Mar 2006 Posts: 80 Location: Eagan, MN

It seems that every time I set a dimmer switch, whether it be in a room or on a fixture, to a setting other than high or off, there is a humming sound.

Why is there a humming sound? It is really irritating! Evil or Very Mad

webmaster · Posted: Wed Oct 11, 2006 5:26 pm Post subject:

Assuming this is an incandescent bulb, the humming is actually the bulb filament vibrating...this is cause by the dimmer switch, but certain bulbs can make it worse!

Contrary to what you may think, modern dimmers work by cutting the power to the bulb on and off at a high frequency, not by changing the amount of electricity going to the bulb (this is the old resistor dimmer that used more electricity and cause much heat). This frequency is high enough that the human eye interprets it as a reduction/increase in light intensity. This pulsation of electricity makes the bulb filament shake or vibrate, because the filament creates a magnetic field and that field fluctuates. With normal AC current the fluctuations are gradual and you can't notice them, but when this power is chopped up by a dimmer switch the fluctuations get worse as the filament is rapidly drawn and repelled to the thin metal post that hold it in place. The end result is audible humming, and sometimes a reduction in bulb life.

So how do you fix it? You could one of the following:

Get different bulbs! You can get Rough Service bulbs that have sturdier supports for the filaments. Halogen bulbs have sturdier filaments also, but make sure they are suitable for your fixture! Halogen bulbs are much hotter and have caused many fires! In addition to these bulbs you can now purchase florescent bulbs that are dimable...they won't hum because they don't have filaments!
Change the dimmer! You probably have a cheaper dimmer that doesn't have the internal devices to correct this problem. High-end dimmers have inductor chokes and interference capacitors to smooth out the sharp jumps in electricity caused by dimmer.

Hope this helps! (Even though it may cost you some money!)

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