I have recently put some smart LED bulbs into my ceiling fan (Lifx if the brand matters) and there is a bad humming noise. Previously there was some humming in at least one of the LED bulbs (they weren't all the same and I don't recall how many made it) but it was much more faint.

I have read that the issue may be the dimmer switch the lights are on, that it may need to be replaced with a special dimmer switch that works with LEDs. How can I tell if my switch is one of these dimmable LED switches or not? Can I tell by looking? I have a very basic multimeter but that is my only tool.

It is worth mentioning that I am aware that now that I have smart lights a wall dimmer is not needed as opposed to a normal switch (dimming is done through the app). If I do end up replacing this switch I will probably put in a "normal" switch instead of an LED dimmer. At this point I am merely trying to diagnose the problem.

  • Hello, and welcome to Home Improvement. You can't test for this (well, perhaps with an oscilloscope); you need to check with the manufacturer. Apr 30, 2019 at 18:56
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    More dimmers are LED compatible without being specifically listed as such. Watch out for bulbs tho, unless the bulb states it’s dimmable it probably isn’t.
    – Tyson
    Apr 30, 2019 at 19:13
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    @CaptainMan It depends on the dimmer. Some dimmers have a "hard stop" at the top of the dimming range which is a mechanical switch that bypasses the dimmer electronics entirely and gives full-shot line voltage to the bulb. However that is a feature in a minority of dimmers, and is usually past a stiff "detent", so many who have it do not realize it exists. Generally dimmer+smart bulb is such a bad combo that there's no profit in trying to troubleshoot it. Apr 30, 2019 at 19:57
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    I get your point about not answering, since your solution wasn't the "answer" to the original question, however, it would help other users and the system to know that this has an answer. Even if it's a bit sideways.
    – FreeMan
    Jun 26, 2020 at 13:42
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    @FreeMan good point. I have marked the answer given as accepted (since it did help me solve the problem), I don't want to post mine and accept as it might be viewed as moving goal posts. I will post mine as an answer though. Jun 26, 2020 at 13:47

2 Answers 2


As a general rule:

  • Incandescent bulbs - will dim with any dimmer
  • Fluorescent bulbs - require a dimmer-compatible bulb and a compatible dimmer
  • "Simple" LED bulbs/fixtures (i.e., not much difference whether fixture + bulb or "all in one") - require a dimmer-compatible bulb/fixture and a compatible dimmer
  • "Smart" LED bulbs/fixtures (and technically speaking, smart "any" bulb or fixture, but normally only found with LEDs for a number of technical & economic reasons that are irrelevant at the moment) - normally require "full" power and any dimming will be handled inside the bulb/fixture.

In addition, as Harper pointed out, there are certain locations (especially stairwells for obvious reasons, but also in general "one per room") where there is an expectation, and code requirement, for a light switch to function to turn lights on/off (unless you just leave lights on all the time - which is practical in some situations). The catch is that if you use an ordinary switch with a smart bulb *and the bulb defaults to "off" when power is initially applied, or remembers previous setting, even if that was "off") then you could end up with the following situation:

  • Person A turns on switch and then turns on light to desired setting via an App or remote control.
  • Person B turns off light via switch - no power = no light.
  • Person C walks in (at night) and turns on switch - and nothing happens. And trips over the remote control that A left on the floor (or whatever...)

This is not a problem with:

  • Secondary lights - e.g., ceiling light has a regular switch (or a permanently installed wall smart switch) and the smart bulbs are in table or floor lamps as an additional source of light
  • Smart bulb defaults to "on" after any full power cycle (this may indeed be the default on some (many? all?) smart bulbs, but it is critical for safe operation if the smart bulbs are the only light on the primary switched circuit.
  • Wall switch is itself a functional remote for the smart bulbs.
  • Thanks for pointing out about code. My other bulbs (Hue brand) can set default power on behavior to be just on (which honestly is best so guests don't have to download some app) but these return to last state (which could be off) unless you do a special pattern (off-on-off-on). Is that a problem? It's my house, not sure if that makes it "okay". Apr 30, 2019 at 19:23
  • @CaptainMan Yes, what you have with Hue - set default power on behavior to "on" is the ideal setup. Anything else is questionable with respect to code compliance. Apr 30, 2019 at 19:41
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    @CaptainMan It's your house and you know how everything works. If, however, EMTs have to show up at 3am, they won't know how it works and they might like some light to work by. Sure, they've probably got flashlights, but overhead lighting makes their work easier, especially when your life may be on the line.
    – FreeMan
    Jun 26, 2020 at 13:41

Replacing the dimmer switch (whichever kind it may have been) with a normal switch fixed the problem. Mentioning this in case anyone with this issue with their smart lights stumble on this.

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