Why do LED lights flickers when seen on film/camera?
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LED lights cycle at whatever the electrical system’s frequency rate is. If it’s on a 60hz system, then it will flicker 60 times a second. Sometimes the camera shutter and the flicker of the light will synchronize.
A lot of LED arrays use something called multiplexing to light up more LEDs than it has the voltage to be able to. It does this by lighting only a few of them for a split second, then switch to lighting other LEDs, then right back to the first LEDs to power them again before they’ve completely dimmed.
To the naked eye, the lights aren’t turning on and off again, it’s continuous light, but a cameras shutter can pick it up.
For the most part, electricity is delivered not as flowing stream but as a back-and-forth wobbling of electrons, called “alternating current”. The rate of this wobbling is fixed by the producer (like, at a powerplant level) and varies by arbitrary national standards but it’s very often in the 50-60 wobbles-per-second range.
This wobbling causes a number of noticeable effects in real life; in electronic signals it can create a humming distortion, like a SHHHHHHH, (special guitar picks called “humbuckers” prevent this in electric guitars), in electric “gear” (power transformers and large devices) it can create an actual loud HUMMMMMM sound that makes electrical stations and rooms loud, in overhead office lighting (the cause of the old fluorescent bulb flickering headaches) and in the case of the LED lights, also, a flickering effect. Basically with each wobble the light turns off for a fraction of a second. If there are 60 wobbles-per-second that gives you an idea of briefly the light is “out” for.
BUT if you have something like a camera that is also an electronic device taking pictures 50-60 times per second you can end up *seeing* the flickering happen if it just happens to be oddly synced with the shutter on the camera. It’s sort of like a strobe effect.
Notice that this effect is most common in bright lighting conditions, because the easiest way for digital video sensors to adapt to brightness is to vary the exposure time. In sunlight they might only be capturing light for a thousandth of a second, doing so 60 times per second. As the LEDs are turning on and off quickly, it can happen that the camera isn’t capturing light at the same time as the LEDs are producing it. Generally the camera and LEDs work at different rates, so sometimes the camera sees the LEDs and sometimes not, giving a flickering effect that’s much slower than the real rates of flickering.
It’s like two cars with their indicators on: sometimes they’re in sync and then a little while later they’re out of sync. The indicators flash relatively quickly but they go in and out of sync over a much longer cycle.
In dim lighting, video cameras are capturing light most of the time so LED flickering effects are much less noticeable.
Normal old school light bulbs are also flickering. Often its usually because the power supply from the output changes its mind about the charge 60 times a second. You cant see the old school light bulbs flicker because the hot filament inside stays hot. Being hot makes it emit light even without power – for a little while!
LEDs don’t heat up. They make light by a different process and can actually turn off & on extremely quickly. Billions of times a second. So they can turn off as the electricity going to them cuts in & out 50 times a second. Also, electronics try to do ‘multiplexing’ as another poster mentioned here, but because LEDs are so responsive we can visually see when its not done fast enough.
A phosphor (not to be confused with Phosphorous, that chemical) is a special coating which illuminates when energy hits it from somewhere. Like an electron or even another light. Normally they’re quite slow to light up & go dim again. Very much like a light bulb Filament staying hot. Old school CRT televisions have this, white LEDs have this. Old school radars have one too (a very slow one, so you can see that BLeeep stay on the screen for ages).
Now coloured LEDs are more basic than white ones (monochromatic is the word). Red/blue etc will be EXTREMELY quick at turning on & off. A white LED actually has a tiny Phosphor coating which eats up light from a hidden blue LED behind it, and then glows as yellowish. It looks white to our eyes. (Its true!) But they are still extremely fast compared to a light bulb.
There are other kinds of lights too: Florescent lights (those tube things) They have yet another way of making light. They need to be stimulated with energy and then you gotta take the energy away. Its when the energy goes away they chill the F out and release a little bit of light. Do this repeatedly real fast and you can get them to keep emitting light, but they flicker.
Truth of the matter is those tube lights are capable of flickering much faster and being way smoother, and the headaches they’ve given people for decades have been avoidable this entire time. In fact, they’re more efficient when you do so. It just cost more money to build the electronics. And we all like to save money if it means we can give people headaches.
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