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I have just had some 230V GU10 LED downlights installed in my living room (by a professional) to replace a traditional pendant fitting.

At the same time, we added a (mechanical) dimmer, however it gives off a very audible buzz from the switch and the light fittings on anything but full.

The light fittings and bulbs are all rated as dimmable, and the dimmer is specifically designed for mains-voltage LEDs, I'm told that this is an unfortunate by-product of using a mechanical dimmer; every dimmer switch I've ever owned has given off an audible hum, but not to this extent and never from the light fittings as well as the switch. There is a second adjustment fine-tune pot on the back of the dimmer, however this is for adjusting in case of flicker, and does nothing but "shift" the hum to different brightnesses.

So, my question is twofold: is the above valid? Are there alternatives, like some kind of switch with 3 positions (e.g. off/low/hi) that may not give off the same hum?

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    Yes, there are digital dimmers. Lutron being one of several manufacturers: lutron.com/en-US/Products/Pages/StandAloneControls/… – DA01 Jul 30 '13 at 21:50
  • I'd ask the professional who installed the lights. – mike Jul 30 '13 at 23:46
  • I've had a few dimmers that hummed, then I replaced them! I'm in the US using 110v but I was always taught a humming dimmer switch was not a good thing. – Jason Jul 31 '13 at 0:14
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As far as I know humming is produced mainly in the core of inductions (coils, transformers) built into dimmers and voltage converters.

Unfortunately all of these 230V LEDs have their own voltage converters, with dimmeable LED's usually sensing the phase cut angle and adjusting the LED chip current accordingly. So you probably may not overcome the humming inside the LED itself. Maybe the only way to have humming free LED light is to use LED bulbs without any current shaping electronics (e.g. 350 or 700mA LEDs) and matching PWM dimmers.

As far as the dimmer is concerned, there are products from Osram, Tridonic and others that are fully solid state electronics, well encapsulated and shouldn't produce humm by themselves. They work on bus systems (DALI, 10V, KNX/EIB) as well as on tap switches.

Regarding off/lo/high ... Ledon produces a LED bulb with "double click" feature, where you use an ordinary on/off switch to switch between off, 30% and 100% ... I saw it in operation recently - very sexy ... other manufacturers are following - search the net for "double click light"

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As is evident by the great answers already given, dimming LED bulbs is not simple!

My story: I purchased dimmable 120v LED bulbs from a reputable manufacturer (Soraa) and attempted to dim them with the Leviton IPI06-1LM dimmer I had used with halogens. Dimming worked, but all four bulbs in the fixture quietly buzzed and occasionally flickered. I then replaced my dimmer with a Leviton C22-06672-1LW, sold as "LED compatible." This reliably dimmed the lamps, but the bulbs still buzzed in almost the same way as with my original dimmer, even at the maximum and minimum dimmer switch settings. It's not a loud buzz, but it disturbs my quiet reading environment.

Research revealed that:

  • The buzzing problem when dimming LEDs is widely discussed online, but there are conflicting solutions;
  • Conventional dimmers use a magnetic tranformer, but line-voltage LED bulbs (the kind you can power with house current) use an electronic "driver" circuit to convert AC to DC electricity;
  • Apparently, mixing magnetic transformers with this electronic driver risks buzzing due to the interaction of waveforms (see The Challenges of Dimming White Paper);
  • When assessing compatibility, rather than insist on complete silence, manufacturers may rely on an acceptable level standard regarding buzzing loudness;
  • Manufacturers offer ELV (Electronic Low Voltage) dimmer switches which use an electronic rather than a magnetic transformer to adjust waveform. These dimmers are more than twice as expensive as conventional ones, but are the only ones consistently reported online as eliminating all buzzing.

Putting all this together, my conclusion at present is that my best chance of obtaining completely buzz-free LED dimming is to purchase an expensive ELV dimmer. I suspect that as the truth becomes known demand for ELV dimmers will rise and the price will decrease. It also appears the technology is still evolving in this area. For now I've therefore reverted to my original Leviton IPI06-1LM dimmer and am bearing the buzz.

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    Conventional dimmers used for the past 30 years are scr or triac driven, verrry high end applications did use a variac this is a variable transformer but of all methods the variac is the only one that has no buzz as the wave form is not affected there is not a laminated core two buzz, – Ed Beal Oct 27 '17 at 19:19

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