Electrical – How to tell if a dimmer switch is LED compatible

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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.

Best Answer

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.
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