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Persistence of vision test with LEDs

Back in the 1980’s, there was a catalogue called “Innovations“. It was full of all sorts of gif gadgets and nic-nacs. I was always fascinated by a clock that looked like a metronome. As the arm moved backwards and forwards, it seemed to spear the time in light in thin are. This was my first introduction to persistence of vision (aka POV). Essentially you eyes not keeping up with reality and leaving slug trails of light on your retinas.

I had a thought… would it also work if the clock arm stayed still and your head moved from side to side? Could I install a single column of flashing LED lights and create POV images in your vision?

The image above is my first experiment. 9 LEDs in a strip, merrily flashing away and me moving a camera with a relatively slow shutter speed from left to right. It does actually replicate what I saw with my actual, organic eyes but saves on the pounding headache I induced will testing it. Turns out heads aren’t supposed to change direction that quickly.

Here are two other images that show it goofing up slightly as you can get a better idea of what’s going on.

The slight flaw in my plan was that those clocks (and the funky LED wheels) take advantage of a sync point. I.e. each tick of a clock resets the flashing so that the lights smear in a repeated, exact position each time. With a shaking head, there is no syncing up between the lights and the head. Each time the head moves, the lights may be flashing a different part of the message, so it’s hit and miss as to whether you see the full pattern or some crossover bewteen the start and the end.

Either way, it works. Just go to build one 200 feet tall…


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