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Related: Dimmer switch gets very warm - almost hot

I have a 3-up light fitting controlled by a dimmer switch. It used to contain 3x40W incandescent bulbs. I recently replaced these with 3x5W LED bulbs marketed as "dimmable". On one occasion after this, I've noticed the switch becoming very hot to the touch when the light has been on for a few hours. Is it possible this is the result of an incompatibility between this particular dimmer switch and LEDs, or is it a fault in the switch that I should report to my landlord?

TIA

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    A simple test is to replace with the old bulbs. If switch still gets hot, then it is the switch. If switch does not get hot, then a problem with the switch and LEDs. Do this when you are staying around, nasty stuff might happen if you leave for hours.
    – crip659
    Jan 23 at 12:34
  • @crip659 Good suggestion, although the overheating is not reproducible with the LEDs, i.e. it doesn't happen every time they're used, so that test won't tell us anything with certainty.
    – Daniel Hatton
    Jan 23 at 12:52
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    I might want to check that all wire connections are tight. Loose connections can cause heat, since resistance is higher. Not usually normal for switches to get warm or worst hot. Having a landlord means most stuff needs a licensed electrician to do, but think checking tightness of connections almost okay.
    – crip659
    Jan 23 at 13:00

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A dimmer for an led bulb is quite different from an incandescent bulb. Generally, the incandescent dimmers lower the voltage. Led lights are actually a circuit and will not work with a lowered voltage. Instead, they use some sort of modulation to keep the voltage the same but interrupt it to reduce the power delivered to the led.

I found this

  1. If you try to dim LEDs with an incandescent dimmer, they get very heated and could catch fire, or the bulbs may explode.

From brightbulb.com

Even if they don't catch fire, their life expectancy will reduce dramatically.

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  • Hmm. I've previously read half a dozen guides to the use of LEDs with dimmers, and the one you link is the first to mention that explosion risk.
    – Daniel Hatton
    Jan 23 at 13:23
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    It happened to be the second site I read. And I can confirm that LEDs are very particular/fragile especially when connected to dimmers. I have replaced enough at my house. If it's getting hot to the touch then there is something wrong.
    – Rohit Gupta
    Jan 23 at 13:35
  • Has anyone seen an LED bulb explode due to dimming? I imagine it would be quite spectacular. More plausibly an internal component might explode, not the whole bulb overall, still making the bulb useless in a less spectacular fashion.
    – user253751
    Jan 23 at 15:34
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    Incandescent dimmers do not "lower the voltage". Your typical incandescent dimmer is a "phase cut dimmer" which works by chopping the mains sine-wave voltage into smaller pieces, resulting in lower power being delivered.
    – brhans
    Jan 23 at 15:43
  • More specifically they tend to be leading-edge or trailing-edge triac dimmers, because that was the cheapest way to make a dimmer in 1973. Those have a very particular waveform, and "dimmable" LED drivers know how to reverse engineer that waveform to figure out what the dimmer is trying to ask for, and manipulate its output to deliver that.
    – Harper - Reinstate Monica
    Jan 23 at 23:03

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