The bulb is fine at full brightness and flickers, strobes or buzzes when you dim it. This is one of the most common smart lighting complaints and the cause is nearly always something in the circuit that should not be there, or a bulb being asked to go dimmer than it can manage.
The short answer
If there is a dimmer switch on the wall, that is almost certainly the problem. A smart bulb does its own dimming and must be fed full mains voltage, so an old dimmer chopping the supply fights it. Replace the wall dimmer with an ordinary switch and the flicker usually disappears entirely.
The wall dimmer conflict
A traditional dimmer works by cutting part of each mains cycle, which reduces the average power reaching an incandescent bulb. A smart bulb does not work that way: it takes full mains voltage, converts it to low-voltage DC, and dims the LEDs electronically.
Put the two together and the bulb receives a chopped supply it was never designed for. Its power circuitry struggles, and the result is flicker, buzzing, unreliable dimming, or a bulb that will not turn on at all at low settings.
The fix is to remove the wall dimmer and fit a plain switch, leaving all dimming to the bulb. Smart bulbs also need constant power to stay on the network, so a wall dimmer turned down is cutting their connection as well as their light.
Check for a dimmer switch on the wall
Look at the switch controlling that light. Any rotary knob, slider or touch dimmer is a problem. This is the cause most of the time and everything else is secondary.
Set any wall dimmer to maximum as a test
Before changing anything, turn the dimmer fully up. If the flicker stops, you have confirmed the diagnosis without any work.
Replace the dimmer with a plain switch
Leave the dimming to the bulb, which is what it was designed for. Unless you are competent and permitted to do mains work where you live, this is an electrician job and a short one.
Check the minimum brightness the bulb supports
Many smart bulbs cannot go below about ten percent cleanly, and below that they flicker or cut out. If the flicker only happens at the very bottom of the range, set a minimum in the app or simply avoid that range.
Update the bulb firmware
Dimming curves are implemented in firmware and low-brightness behaviour has been improved in updates on several platforms. Check every bulb updated, not just the one you noticed.
Check for mixed bulbs in one fitting
Different models dim differently. A fitting with two bulb types will show one flickering while the other is steady, and no setting reconciles them.
Check the fitting is not enclosed
An enclosed shade traps heat, and heat makes the bulb’s driver circuitry behave badly, including flicker. Check whether the bulb is rated for enclosed fixtures, because many are not.
Try the bulb in a different fitting
If it flickers in one fitting and not another, the fitting or its switch is at fault rather than the bulb. This takes two minutes and settles it.
Do not work on mains wiring unless you are competent and permitted to do so where you live. Replacing a wall dimmer with a switch is a short job for an electrician and not worth risking. Checking what type of switch is fitted, and turning a dimmer to maximum, are both perfectly safe.
Flicker you can see and flicker you cannot
Some LED flicker is fast enough that you do not consciously see it but it is still there, and it is a known cause of headaches and eye strain for some people. A quick way to check: point your phone camera at the bulb and look at the screen. Rolling bands or a visible pulse that you cannot see with your eyes means the bulb is flickering rapidly.
Cheap bulbs flicker more than good ones, and it tends to be worst at low brightness where the dimming is done by switching the LEDs on and off rapidly. If someone in the house gets headaches in a particular room, this is worth checking before assuming it is unrelated.
If a smart bulb is on a circuit where someone will inevitably use the wall switch, consider a smart switch instead of smart bulbs. A smart bulb switched off at the wall is offline and unreachable, which frustrates everyone. A smart switch keeps control at the wall and in the app at once, and it works with ordinary bulbs.
Buzzing rather than flickering
An audible buzz or hum from a dimmed bulb has the same root cause: the driver circuitry working in conditions it was not designed for. A wall dimmer is again the usual culprit. It can also come from the dimmer itself rather than the bulb, so listen carefully to establish which is making the noise before replacing anything.
Some buzzing is inherent to cheaper bulbs at low brightness and cannot be fixed. If it persists with a plain wall switch and updated firmware, the bulb is simply built that way.
Can I use smart bulbs with a dimmer switch?
No. Smart bulbs need full mains voltage and do their own dimming. A wall dimmer chopping the supply causes flicker, buzzing and unreliable operation. Replace it with a plain switch.
Why does my bulb flicker only at low brightness?
Many bulbs cannot dim below about ten percent cleanly. Below that the driver struggles and you get flicker. Set a minimum brightness in the app or stay above that range.
Should I use smart bulbs or a smart switch?
Use a smart switch where people will use the wall switch out of habit, since a smart bulb switched off at the wall is offline. Use smart bulbs where you want colour or per-bulb control.
Can I put smart bulbs in an enclosed fitting?
Only if they are rated for it, and many are not. Trapped heat shortens their life and causes exactly this kind of erratic behaviour.
Why does the bulb buzz when dimmed?
The same cause as flicker: the driver circuitry operating outside its design conditions, usually because a wall dimmer is in the circuit. Listen carefully to check whether the noise is the bulb or the dimmer itself.
The bottom line
Look at the wall switch first, because a dimmer in the circuit is the cause most of the time and turning it to maximum confirms it in seconds. Replace it with a plain switch and let the bulb do its own dimming. If flicker only appears at the very bottom of the range, the bulb has simply reached its limit and setting a minimum brightness is the answer.
