Because your camera looks differently from your eye. Almost every LED switches on and off hundreds of times a second, and your eye averages that away. A camera takes short snapshots and therefore sees dark bands or a light that appears to pulse.
Why an LED flickers without you seeing it
An LED runs on direct current, but the socket delivers 50 hertz alternating current. The driver converts that, and how well it does so varies a lot. If ripple is left on the direct voltage, the light output varies along with it.
On top of that, many drivers dim using pulse width modulation: they switch the LED on and off extremely fast and set the brightness with the ratio between the two. At full output you do not notice. When dimming, the gaps get longer and the effect becomes more visible.
What the camera does with it
Almost every phone camera has a rolling shutter: the sensor is read out line by line instead of all at once. So every line catches a slightly different moment. If the light pulses faster than that readout, one line gets more light than the next and you see horizontal bands across your shot.
Video adds another effect. If the frame rate and the light frequency do not line up neatly, the whole image slowly swells and fades. That is why a kitchen that looks perfectly fine to the naked eye looks restless on film.
There are legal limits
Since 1 September 2021 the European Ecodesign regulation (EU) 2019/2020 sets requirements on flicker. There are two measures:
- PstLM for visible flicker. The limit is 1.0. At exactly 1.0 an average observer has a fifty percent chance of noticing the flicker.
- SVM for the stroboscopic effect, so what you see on moving objects. The limit is 0.4, tightened on 1 September 2024.
Those requirements apply to the light source at full output. As soon as there is a dimmer in between that does not suit the lamp, the manufacturer no longer stands behind it. That is precisely where most complaints come from.
Why dimming makes it worse
A dimmer cuts a slice off every half wave. So less power arrives, and the driver has to make something of it. Below the dimmer's minimum load, the driver gets so little to work with that the output starts pulsing.
That is why our LED dimmer from 0.5 to 250W and the version up to 160W start at half a watt instead of at the forty watts of an old incandescent dimmer. Hang a single 6 watt spot on a dimmer that only works from 40 watts and flicker is guaranteed.
More on that in Which LED dimmer do you need for your spotlights? and Why does your LED lamp flicker?
What you can do about it
For the filming itself: set the shutter speed to a multiple of 1/50 second, so 1/50 or 1/100. Many phones have a setting for this called anti-flicker or 50 Hz. That fixes the image, but not the cause.
For the installation: choose a driver that runs at full output rather than dimmed, or dim on the direct current side. Our 12 volt drivers control the light after conversion, by remote, rather than by chopping the mains voltage.
If you notice the flicker with the naked eye as well, something is genuinely wrong. That is not a matter of taste but of a light source that does not meet the standard, or a dimmer that does not suit it. The spots are at recessed spotlights.
Is flickering LED light harmful?
Visible flicker is associated with headaches and fatigue. That is why there has been a European limit since 2021, with PstLM 1.0 and SVM 0.4 as maxima.
Why do I see stripes in a photo of my ceiling spots?
Your camera's sensor is read out line by line. If the light pulses faster than that readout, each line catches a different moment and you get banding.
Does a dimmed LED flicker more than an undimmed one?
Usually yes. The European requirement applies at full output. When dimming, the gaps between the pulses get longer and the effect shows up on camera sooner.