ELI5- why do screens/lights flicker in videos taken by phone or even yt vids, but not in movies and professional productions?
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Lights and screens blink 50 times in one second in places like Europe, or 60 times in a second in places like the US, because of how electricity is sent through your country (this is called the *refresh rate*). You can’t see this with the naked eye, but your camera can.
Phones normally take one frame 60 (or 30) times in a second (because they’re made in places where that’s the normal refresh rate of electricity – this is called the *shutter speed*), while professional cameras can come in more shapes, sizes and (most importantly) *things you can change manually.*
If you are in Europe and filming with a smartphone made in California, the speed at which your phone camera and the lights or screen that you’re filming refresh will not match, resulting in that flickering effect. Most of the time you can’t change this on your phone without getting some app to do it manually. This mismatch only gets worse with slow-motion video (regardless where you live).
Movie cameras can adjust pretty much everything about how they’re filmed manually, meaning they can correct for this kind of problem by changing the shutter speed to sync with the refresh rate it’s filming.
Shutter speed of the camera vs refresh speed of the screen. Your camera doesn’t take an image instantly. Instead it goes down row by row kinda like a printer. Your monitor does the same thing. When these two speeds line up poorly they cause the flickering. You don’t see this in movies cause they can do tricks like CGIing in the screens later, rotate the camera so the camera is going left to right instead of top to bottom, or you can get cameras that can sync with screen refresh rates to eliminate the flicker.
What he means by synched cameras is that the film rate matches the refresh rate of the screen being filmed, if you match your fps to the refresh rate you don’t see the “flicker”
What he means by synched cameras is that the film rate matches the refresh rate of the screen being filmed, if you match your fps to the refresh rate you don’t see the “flicker”
in addition to all the great answers, you might be interested in this modern use of the synchronized refresh rate / recording — [https://www.reddit.com/r/nextfuckinglevel/comments/odmy22/different_channels_different_ads/](https://www.reddit.com/r/nextfuckinglevel/comments/odmy22/different_channels_different_ads/)
several different commercials are played at the same time, on the same screen. it’s recorded in a high frame rate, and broadcast in a low framerate. so different broadcasters can choose a different frame offset.
Today, CGI is often used. I worked with a Mac II (circa 1989) that was going to be filmed and the film-makers brought a special video card that allowed the video generated to be synced with the camera. It filmed rocked solid.
Explaining like your five? Here we go…
Funny enough, all man-made light flickers, or turns off and on really really fast. Our eyes see at about 24 frames, or pictures, in one second. That’s why when things move faster than that, it looks blurry, kind of like why helicopter blades or the hubcaps of cars blur in motion.
Now, ever turn on your fan, and it goes faster and faster, then it looks like it’s moving backwards? That’s because the fan is turning so fast, your eyes only see the fan 24 times a second. So when your eye sees it the next time, the fans blades are in a different position, and it ‘appears’ to move backwards!
Now, with certain cameras, you can adjust something called “shutter speed”. When you take a picture, the shutter speed is basically how long the camera ‘blinks’ in a second.
So blink right now. That’s like taking a picture.
Now blink really fast! That’s what a video camera is doing. It’s taking pictures and putting them together. That’s the basics of a video.
And you can tell both cameras to ‘blink slower’ or ‘blink faster’.
Now, TV’s and monitors and even florescent light ‘blinks’ at a certain speed. If you tell your camera the blink at the same speed, your camera will show you what your eyes see…a steady light, or a spinning fan, or a solid glowing computer screen.
If you tell your camera to blink at a DIFFERENT speed, your camera can show you all kinds of things—a blinking computer monitor, or fluorescent light being red instead of white. You can even make a flying helicopter look like a floating without turning the blades!
Go ahead and try it out!
Lights aren’t “turned on” without any pause. They all flicker a bit because of the electricity supply, but this flickering is too fast for our eyes to notice.
Every camera also does not record without any pause, it takes an image, then after some time takes another.
When the camera takes images faster than the time it takes for a screen to “shine then pause/rest then shine again”, then you end up seeing these on recordings as an annoying flicker; originally the reason cameras take so many images so fast is because the film gets very “smooth” and motion is captured in much more detail, but these annoying flickers from screens is the drawkback of this feature. Theoretically, there are 2 ways to avoid this: 1 you record slower (there are various ways to do this) so the flickering vanishes or 2 you give shorter pause /rest time for the screens. In practice obviously we go with scenario 1, because if you tamper with the electricity supply of the electronics by yourself, you could break it and even hurt someone.
Some light bulbs don’t necessarily flicker, because instead of rapidly turning off for a moment then on again, instead it faintly gets dimmer then brighter (you can do this with smart placements of diodes in the circuit to smooth out the electric supply to a relatively almost constant current; I believe more household light bulbs are made this way if you buy new generation, but I’m not sure) and the camera may not necessarily pick up this faint back-and-forth switches.
This is just roughly the theory to why you see it and how you could in principle overcome this. I don’t actually work in filming, so the current methods and solutions are definitely more smarter, but I don’t believe an ELI5 answer should reference anything too technical.
More expensive lightbulbs can be made to not flicker, dispite the alternating current in your wall outlet.
First off, lights connected through an outlet aren’t always on, the flicker to the frequency of your grid, so 50-60 hz depending on where you live, some cameras record in 25fps, with a 50hz system every frame will have light as 50 is a multiple of 25, on the other hand a camera recording at 25fps and a grid on 60hz will not match and this you will see flickering of lights when you record. That is a similar issue recording refresh rates on screens and cameras again. On most cameras you can change your fps to 25 (PAL option on iPhone) to accommodate for the flickering.
Production companies will makes sure that everything matches plus they have post production and what not
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