Recently, I installed a regular light switch with a slide dimmer next to it for my bathroom light (inexpensive 3 40-watt bulbs on a metal box), so when I get up in the night, I can turn the light on and see, without frying my retinas...

But ever since I installed the switch, there is a 'hum' from the lights--even when the dimmer is on full. This did not happen with the ordinary light switch.

Is there anything I can do to keep the dimmer and minimize (or eliminiate) the hum?


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Tim Green
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If the hum is really coming from the bulbs then it is possible that the filaments are vibrating at 60Hz and this vibration is perhaps amplified by a natural mechanical resonance of the enclosure. The fact that it hums even when it is on-full, indicates that the dimmer is not delivering the full sinewave, in other words is switching at < 180 degree. To prove this point measure the AC voltage (Vrms) before the dimmer and after the dimmer. If this is the case, you should notice a measurable voltage decrease after the dimmer on-full position. To diminish the hum try experimenting by changing the natural frequency of the enclosure.


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A quality dimmer is often the right answer. Very cheap (or no) filtering of the dimmers output causes louder humming. High quality units have an ~1" coil that reduces filament hum dramatically.

Mostly these dimmers come in the large "decorator" style faceplate. Yours sounds like Lutrons "Ariadni" try their "Diva" instead.

Richard Reid, LC

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