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Name: Edward M.
Status: educator
Age: 50s
Location: N/A
Country: N/A
Date: 2001-2002


Question:
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.

Vince Calder


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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