Is flickerless AC dimming possible?

I use this RobotDyn AC dimmer module with ESPHome, and the brightness is close to constant but not quite. It has a minor flicker that is not instantly noticeable but slightly disturbing long-term. Is this to be expected?

My sense is that AC dimming is a messy solution because rather than directly controlling the LEDs, there’s an intermediate power supply of the bulb driven by AC voltage, which is not designed with high-quality dimming in mind, not even for dimmable bulbs.

My configuration:

  board: az-delivery-devkit-v4
    type: arduino

  - platform: ac_dimmer
    id: dimmer1
    gate_pin: 16
    method: leading
    init_with_half_cycle: false
      number: 17
        input: true
      inverted: yes

  - platform: monochromatic
    output: dimmer1
    name: Dimmerized Light

I’ve tried all 4 relevant combinations of the method and init_with_half_cycle parameters, and I’ve also tried 2 dimmable bulbs, but I haven’t achieved constant dimming without minor flickers.

I’m interested in your experience in general and in specific with various dimmable bulbs and dimmers.

TL;DR It’s complicated. Try more different bulbs.

Mains voltage LED bulbs have internal circuitry to rectify and drop supply voltage to that suitable for LEDs. That could be 2V, or more likely, arrays of series LEDs going up to (say) 100VDC.

Some bulbs use dumb capacitive droppers, some use constant voltage, some constant current - buck/ boost buck chips are now almost ubiquitous.

Connecting complex and varied PSUs to simple phase-angle controllers isn’t going to work every time. Fibaro FGD-212 dimmers can use leading edge or trailing edge control, depending on auto-detection and still don’t work always (especially at low levels). Some dimmers even act like VFD phase converters and vary AC frequency.

There’s lots of BigClive videos on YouTube where he reverse engineers bulbs from £1 to £1k. The circuitry may look similar, but many work differently.

Expensive Philips LEDs sometimes work, cheap IKEA LEDs also sometimes work. It’s complicated! :man_shrugging:t2: :mage:t2:


Long before I had any ‘smart’ things in my house, I put in ‘dimmable’ can lights and literally went through every dimmer sold at my local store and had flickering with them all. It was a dedicated circuit and I even had a friend who is an electrician take a look to make sure I wasn’t doing something stupid (he actually installed those exact lights all the time with no issues).

I finally gave up and it happened to be the thing that got me to jump into Phillips Hue bulbs. Luckily I was renovating my basement, so the old-new lights got rehomed down there. It was pricey, but worth it as it was just WAY too bright at full-blast pretty much all the time (plus I got a couple color ones to add some fun and it’s been nice to be able to shut off certain lights, like when we have the Christmas tree under one of them). Since then, I’ve just gone with Hue bulbs anywhere I want dimming, which isn’t very often.


+100 on try more bulbs.

Also when you find ones that work buy enough to keep you stocked or you’ll be doing the dance again.

That dimmer is capable of dimming over 3kW of lighting on each channel!

How many watts of LED lighting are you trying to dim?

Triacs need a minimum current to continue conducting, once they are switched on, typically based on their max current rating.
The LED load that is connected, is just likely insufficient.

Try putting a 100w incandescent light bulb connected in parallel with the leds.
If the leds don’t flicker then, I suggest you would be better off changing the controller than ‘trying’ different led bulbs.

(Or maybe leave the 100W bulb connected). :slight_smile:

Having one incandescent bulb in parallel with LEDs does definitely work, especially for dimmers without a Neutral wire (e.g. gives a resistive load for some current to power the 2-wire series dimmer itself).

I found early Fibaro firmware needed an incandescent bulb to work, but ‘fixed’ versions can drive all LED fittings (with the right LEDs…).

I also found the parallel ‘ballast’ shunts didn’t achieve much (think they are an Y1 capacitor and resistor, again to give some current flow).

The challenge these days is the almost complete removal of incandescent bulbs from the market.

My personal preference is for dimming controllers fitted in the wall to keep control via standard switches - something ‘smart bulbs’ need a blanking plate or RF control hiding the dumb switch to achieve.

The extra colours smart bulbs usually offer can be nice for mood lighting or notifications. Sadly the white light can be poor unless you buy decent quality.

Its after 1 September. COMPLETE removal of incandescent and halogen in the US. except special case bulbs.

They did this in Europe over 10 years ago…

Fun fact you can still buy them - not labeled as lamp but as “heat bulbs” :fire:

Long story short: dimmable bulb ≠ dimmable bulb :warning: And dimmamble (led) bulbs might be dimmable to an extend - maybe with limited range and/or flicker included :bulb:

It might be a easier solution in that case to get a “smart” dimmable bulb as this should guarantee a smooth dimming as it is sold as is :shopping:

I been trying to use RobotDyn AC dimmer. I have it working, but have not been able to find a bulb that is flicker free with this device. I’ve had the dimmer connected to both an esp32-wroom and esp8266. When connected to the esp32 flicker is really bad, on the esp8266 it’s almost usable light. Have you found a light bulb you would recommend? Any suggestion on getting a better signal from the esp to the dimmer?

I’ve given up on AC dimmers due to such issues, and I’ve been using Zigbee bulbs with which I’m satisfied. I also plan to use Zigbee LED dimmers with LED strips.