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Can someone ELI5 why often lights set up with a dimmer also flicker? (mander.xyz)

submitted 9 months ago by [email protected] to c/[email protected]

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Seen this in many houses, people upgrade their lighting setup and install a dimmer. Which works. But usually it also makes the lights flicker unintentionally, which is super annoying IMO.

Now, my understanding of electrical engineering is pretty rudimentary so I'd appreciate more something that explains the concept in a way that Cavewoman Mothra can understand rather than something technically accurate.

Thanks

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[–] [email protected] 66 points 9 months ago (11 children)

Power coming into the house is AC which means 50-60 times a second the power goes from +110/240V to -110/240v.

LED lights run off DC power, so to change the power type a capacitor is somewhere that holds enough charge to keep the item working until the AC power is back to a usable positive value.

Dimmers limit the power going to the light, so the capacitor doesn't charge enough to keep the light and circuitry on for the full negative swing of AC power.

This is ungodly rudimentary, and corrections are welcome. There is also many nuances I am missing.

[–] jjagaimo 19 points 9 months ago* (last edited 9 months ago)

Dimmers will typically use a triac which cuts up the sinusoidal waveform. It doesnt actually lower the amplitude per se, but it limits the fraction of the time the waveform is on. Kinda like this. This means that a lot of the time the led isnt gettingas much or any power. The average power will be lower, and if the LED driving circuitry isnt designed to compensate for this, the LED will flicker.

Clarification on triacs: they get turned on a certain fraction of the way into the cycle. Triacs will stay on until the voltage across them is 0. Conveniently the zero-crossing of the AC wave (when the wall voltage crosses zero to start foing negative or from negative to positive) does just that.

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