The short answer
If there is a dimmer switch on the circuit, that is almost certainly the cause: smart bulbs must have a normal on-off switch and full mains voltage. Replace the dimmer with a standard switch. If there is no dimmer, the flicker is the bulb’s own driver, worse at low brightness, and only a better bulb fixes it.
A smart bulb contains its own dimming electronics. It expects full mains voltage at all times and adjusts brightness internally. A wall dimmer works by chopping the mains waveform, which starves those electronics and produces flicker, buzzing, refusal to turn on at low settings, and in some cases premature failure of the bulb.
Cause 1: a dimmer switch on the circuit
This is the most common cause and the most frequently overlooked, because the dimmer may be one the previous occupant fitted and you have never turned past maximum.
Check the switch
A rotary knob, a slider, or a push-button that also rotates is a dimmer. Some look like ordinary switches with a small slider on the side.
Set it to maximum and test
If the flicker stops at full and appears as you turn it down, that confirms it.
Replace it with a standard switch
This is the correct fix. Smart bulbs need constant full voltage, and you dim them in the app, not at the wall.
Or use a smart switch and ordinary bulbs instead
For fixtures with many bulbs or an existing dimmer you want to keep, a smart dimmer switch with plain dimmable LEDs is the better architecture.
Mains wiring is not a place for guesswork. If you are not confident isolating the circuit at the consumer unit and identifying live, neutral and switched live, have an electrician change the switch. It is a short job for them.
Cause 2: the bulb’s own driver
Every LED bulb converts mains AC into the DC its diodes need. Cheap drivers do this with visible ripple, which appears as flicker, particularly at low brightness where the duty cycle is short. Some people perceive it directly, others only as eye strain or headaches, and it usually shows up clearly on a phone camera as banding.
There is no fix other than a better bulb. When shopping, look for mention of flicker-free operation or a low percentage flicker figure. Reputable brands publish this; very cheap bulbs do not.
A practical test: point a phone camera at the bulb at its lowest setting. Heavy banding or rolling lines on the camera preview indicate significant flicker even if your eyes do not register it.
Cause 3: minimum load and mixed circuits
Older dimmers and some relays are designed for incandescent bulbs and expect a minimum load, often 25 to 40 watts. A few LED bulbs drawing 8 watts each do not meet it, and the result is flickering, glowing when off, or erratic behaviour. Where a dimmer must stay, LED-compatible dimmers with a low minimum load exist and are the correct replacement.
Mixing bulb types on one circuit causes its own problems, particularly mixing smart and non-smart or different brands. If one fixture has several bulbs, use identical bulbs throughout.
Cause 4: the neutral problem
Smart switches that do not require a neutral wire work by passing a small current through the bulb even when off. With incandescent bulbs that is invisible. With LEDs, that trickle is enough to make them glow faintly or flicker when off. The fixes are a bypass capacitor fitted at the fixture, which the switch manufacturer supplies, or a switch that uses a neutral wire.
Cause 5: the network, oddly
Occasional flicker at the moment a bulb receives a command is normal, and repeated flicker can indicate a bulb repeatedly reconnecting. On Zigbee and similar mesh networks, a bulb at the edge of range may drop and rejoin, briefly reverting to its default state. Check the bulb’s connection quality in the app, and consider adding a mains-powered device between it and the hub to extend the mesh.
A firmware update is worth applying too, since dimming curves and low-brightness behaviour are firmware-controlled and manufacturers do improve them.
Many smart bulbs have a minimum usable brightness below which they flicker or cut out, typically around 1 to 5 percent. If flicker only occurs at the very bottom of the range, setting a floor of 5 or 10 percent in your automations avoids it entirely and is easier than replacing the bulbs.
Choosing bulbs that behave
- Look for explicit flicker-free claims and published flicker percentages.
- Prefer brands with firmware updates, since dimming behaviour improves over time.
- Check the minimum dimming level in the specification if you use very low light.
- Match bulbs within a fixture, same brand and same model.
- Consider a smart switch plus quality dimmable LEDs for ceiling fixtures, which is often better than smart bulbs and always cheaper for a multi-bulb fitting.
Can I use smart bulbs with a dimmer switch?
No. Smart bulbs need constant full mains voltage and dim internally. A wall dimmer starves their electronics, causing flicker and shortening their life. Replace the dimmer with a standard switch.
Why do my smart bulbs glow faintly when switched off?
Usually a smart switch without a neutral wire passing a small current through the bulb. A bypass capacitor at the fixture, supplied by the switch manufacturer, resolves it.
Is LED flicker harmful?
It is not dangerous, and it causes eye strain, headaches and fatigue in sensitive people, particularly at low brightness. Quality bulbs with proper drivers largely eliminate it.
Why does only one bulb in the fitting flicker?
Bulbs vary between units even within the same model. If everything else on that circuit is fine, swap that bulb with one from another room to confirm whether the fault follows the bulb.
Are smart switches better than smart bulbs?
For ceiling fixtures with several bulbs, usually yes: cheaper, no dimmer conflict, and the wall switch keeps working normally for everyone else. Smart bulbs win where you want colour and per-bulb control.
The short version
Look for a dimmer on the circuit first, because that explains most cases and the fix is replacing it with a standard switch. If there is no dimmer, test with a phone camera at low brightness to confirm driver flicker, and accept that only a better bulb solves it. Set a minimum brightness floor in your automations, keep bulbs matched within a fixture, and consider a smart switch instead for ceiling fittings.
