By Mark J. Donovan
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Question: Mark, I recently installed a new dimmer switch in my home, but
unfortunately when I dim the lights I keep hearing a small humming sound coming
from the lights. Yet when I turn the dimmer switch up to its maximum lighting
level the sound disappears. Please help.
Answer: K.D. In regards to your question about the humming sound you’re hearing
with your dimmer switch there are a few reasons why it may be occurring.
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First, however, it is important to understand how today's modern dimmer
switches work. At the heart of today’s dimmer switches is a Triac, which is a
transistor like type of device. The Triac effectively controls the amount of
voltage a light bulb sees by you adjusting the dimmer slide or knob. With a
normal always on/off light switch a light bulb turns on/off at a 60 Hertz (or
cycles per second) rate when the light switch is left in the on position. To the
naked eye, however, the light bulb appears to be always on when the light switch
is left in the on position.
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With a Triac dimmer switch, however, the on/off power duty cycle time is
adjusted as you control the dimmer slide or knob. When you dim the lights, for
example, the Triac is effectively causing the light bulb to turn on less
frequently, and conversely when you brighten the lights the Triac is causing the
light bulb to turn on more frequently (up to the 60 Hertz rate).
To the naked eye, it looks like the light bulb is burning less brightly when
you lower the dimmer switch, but in reality the light bulb still produces the
same luminosity each time it is turned on. |
It's just that your eyes average out the on/off motion so that you perceive
the light bulb is burning dimmer.
This action of turning the bulb on and off can cause the light bulb filament to
vibrate, which in return produces the humming sound that you are hearing.
| One way to solve this problem is to use lower wattage bulbs
in the light fixture so that they consume less power and thus will not
vibrate as much, at least to a level you won't hear. Another solution is
to use rough service light bulbs that are often used in garages, basements
and appliances such as refrigerators. Rough service light bulbs, or heavy
duty light bulbs, have sturdier
filaments that are less prone to vibrate when fed by a dimmer switch. |
Photo by Mark Donovan |
Finally, you can buy a higher quality dimmer switch that can smooth / filter
out the high current spike draws when the dimmer switch turns the light bulb(s)
on. By smoothing out the ramp in-line current to the bulbs you can prevent the
bulbs from oscillating as much. You may notice however that these types of
dimmer switches feel a little warm to the touch as they have to dissipate a
little bit more of the energy they filter/smooth out.
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