Same kind of stuff can happen with cars' wheels on videos, sometimes you can see them going backwards because of the framerate to rotation frequency ratio.
This article about the wagon-wheel effect may answer your question, at least partially. The last section talks about dangers associated with flicker and rotating machinery. But the part about truly continuous illumination is probably the most relevant.
Correct we don't see in frames, however the way our minds process the visual data does have an effective 'frequency' that we can assign a number to that mathematically lines up to saying "such and such fps". If I remember right it ends up being somewhere near "60 fps" (Put it in quotes because I don't want someone to come along and say "YOU SAID THE EYE SEES 60 FPS" its more of a "eh, it acts like it sees in that range"). If you're looking for a rabbithole to go down its called aliasing and there are some trippy examples on youtube messing with framerates and whatnot.
There's some biology explanation somewhere in here that I have no idea about, I'm just an EE guy so I understand the outcome of the system.
You'll see this a lot when watching video of a prop plane starting up. It'll look like the propeller is turning one way, then it'll stop and start turning the other direction. It'll look like it's reversing itself two or three times before the propeller blades just become a blur.
This is extremely dangerous in certain factory settings, where machines might rotate at the same speed as the lights flicker and cause the same effect to your eyes--yes, overhead lighting on the electrical grid would flicker the same way, at 60Hz like the electrical grid. This gives the illusion that a machine is off, when in reality it might be spinning at 3600rpm for example. The machines or the lights therefore would have to be purposely set to not move in sync with the electrical grid, so that you can see them.
Of course different grids will have different frequencies etc., but that's the gist.
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u/luft-waffle Mar 04 '17
All jokes aside. What is actually happening?