Light Dimmers and Resonance
Name: Edward M.
We have several incandescent bulbs that are controlled by
dimmers. If the dimmers are slowly moved, there are several positions
where the bulb makes a noise. I assume these noises represent some sort
of resonant frequency, but what is vibrating? and what property of the
changing electrical energy is altering the vibration to set up the
resonance? Am I correct in assuming that to maximize bulb life the
dimmer should be set to avoid these noises?
Interesting question. Possible sources might be: 1. A "hum" from the
dimmer -- presumebaly a transformer -- due to the 60 hertz AC current. This
is the very familiar hum you pick up around unshielded AC circuits. 2. The
AC current might set up a vibration in the filament, or its wire leads. This
would be a much higher frequency pitch. If it is the latter, certainly you
would want to avoid those settings.
I do not know, but I would guess the dimmer decreases the portion of the
normal sine wave which will be let through to the bulbs in order to dim
the bulbs. Different portions of a sine wave will have different harmonic
components. When a large harmonic component is at the frequency of a
resonance of the filament, the filament could be made to vibrate more
vigorously and even emit noises. I would say that you are absolutely
right in that those settings should be avoided for maximum bulb life.
Richard J. Plano
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Update: June 2012