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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Moving pictures on an old TV are basically a series of still images strung together (like an updated version of flip cards) The movie camera is taking a series of still images and stringing them together. If the camera and the screen are not working together, you get flickers.
[Beside post production. Tom scott does a good explanation of the effect.](https://www.youtube.com/watch?v=uzP8FFKpwQ0)
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
More expensive lightbulbs can be made to not flicker, dispite the alternating current in your wall outlet.
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.
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!
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.
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.
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”
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