hi guys!! so i had my dimmer working perfectly with a regular incandescent bulb for like 2 weeks. today i swapped it out for an LED bulb because i wanted to save on electricity and now its flickering like crazy!!
the incandescent was a 60W and it dimmed super smooth from 0 to 100. the LED is a 9W bulb i got from the hardware store. when i turn teh dimmer on the LED just flickers non stop, like a strobe light almost. at some power levels its worse than others but it never goes fully smooth.
my setup:
- arduino uno
- rbdimmer 1CH 4A module
- was working perfectly with incandescent
- LED bulb is a regular 9W E27
i didnt change any code or wiring, literally just unscrewed the old bulb and put in the new one. whats going on?? is my dimmer broken now or somthing?
please help!!
Pretty sure this is an EMI/ringing issue on the TRIAC output.
When the TRIAC fires into an LED driver (which is basically a switched-mode power supply), you get high-frequency ringing at the switching point. The LED driver’s input capacitor sees a sudden voltage step and oscillates.
Try adding a snubber circuit across the load — a 100Ω resistor in series with a 100nF capacitor (rated 400V+) connected in parallel with the TRIAC output. This dampens the voltage ringing and can reduce or eliminate the flicker.
Worked for me on a similar setup with a cheap LED panel. YMMV though — depends on the specific LED driver design.
Before going the snubber route, I’d check something more fundamental first.
The issue: Most standard LED bulbs are not compatible with TRIAC (leading-edge) phase-cut dimmers. The problem isn’t noise or ringing — it’s that the LED driver circuit inside the bulb isn’t designed to work with a chopped AC waveform.
Here’s what’s happening:
- A TRIAC dimmer works by cutting the front of each AC half-cycle (leading-edge phase cut)
- Incandescent bulbs are purely resistive — they don’t care about waveform shape
- LED bulbs have an internal driver (basically a small power supply) with input capacitors
- When the TRIAC fires partway through the cycle, the driver’s capacitors see a sudden voltage spike and charge rapidly
- This causes current pulses that can drop below the TRIAC’s holding current, turning it off prematurely
- The TRIAC re-fires, creating visible flicker
A snubber might reduce the symptoms slightly but won’t fix the root cause — the LED driver fundamentally isn’t designed for phase-cut input.
What to look for: LED bulbs specifically labeled “dimmable” have modified driver circuits that handle phase-cut dimming. Regular LED bulbs (even good quality ones) will flicker with any TRIAC dimmer.
ohh ok so its the bulb not the dimmer! thats a relief lol i thought i broke somthing
so if i just buy a bulb that says “dimmable” on the box it should work with my existing setup? i dont need to change any code or wiring?
im gonna go to the store tommorow and look for one. do you guys have any specific brand recomendations? i just want it to work without flickering lol
Yep — no code or wiring changes needed. Just swap the bulb.
For brand recommendations, I’ve had good results with:
- Philips dimmable LED (they explicitly test for TRIAC compatibility)
- IKEA TRÅDFRI dimmable bulbs (surprisingly good for the price)
- Osram/Ledvance dimmable range
Just make sure the packaging says “dimmable” — don’t assume. Two bulbs from the same brand can look identical but one is dimmable and the other isn’t.
One more thing: even with dimmable LEDs, the dimming range is typically narrower than incandescent. You might get smooth dimming from about 15% to 100% instead of 0% to 100%. Below 15% some LEDs will still flicker or just turn off. This is normal — the minimum power threshold is higher for LED drivers.
update!! i got a Philips dimmable LED bulb (it says “dimmable” right on teh box) and IT WORKS!! no flickering at all, smooth dimming just like the old incandescent!
the only thing is like hank said it doenst dim all the way down to zero — below about 20% it just turns off. but thats totally fine for my use case
omg thanks so much everyone!! this forum is amazing!!!
Glad it’s working!
For anyone finding this thread later, one thing worth noting: LED compatibility lists vary by country and region. A bulb that’s labeled “dimmable” in one market might have a different driver in another. If you’re ordering internationally, double-check reviews from your region.
Also, if you need deeper dimming range (below 15-20%), consider the rbdimmer MOSFET module that was mentioned above. Trailing-edge dimming gives a wider usable range with LEDs — some users report smooth dimming down to 5-10% with the same bulbs that cut off at 20% on a TRIAC.
Ah good point from Hank — I stand corrected on the snubber suggestion. A snubber helps with ringing and EMI but wouldn’t fix a fundamental driver incompatibility. The LED driver needs to be designed for phase-cut input in the first place.
Good to know for future reference: dimmable bulb first, snubber only if there’s residual flicker with an already-compatible bulb. Thanks for the correction.