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Why do Lasers leave trails?

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I searched the same question here and on google. Other people had asked the same question but the people that answered it didnt understand the question. They answered it with things like dust in the air reflecting the light. But that explains the beam, not the trails from the a moving laser.
So when twirling a laser while aiming it at a wall it appears to be one continuous circle. Why is this? My thought is that it is burning an image in your eye.
Any scientific info bout this?
 

Eudaimonium

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Same reason you can get "flashblinded" for example.

Ever had a flashlight shined into your face, and you know how you get those dots and shapes floating in your vision for some time?

That's because the eyes do not detect the change in any part of your vision instanteniously, they need time to change the perception (fade, if you will).

EDIT - Hmm going through the materials I linked, seems that's only half of the explanation, other half being the very breif "Iconic" memory. See wiki links for more info.

Zipping the laser quickly across the wall does not produce a moving dot in your perception, it produces a quick-fading line.

Now, about some sources,
Persistence of vision - Wikipedia, the free encyclopedia and more closely related,
Sensory memory - Wikipedia, the free encyclopedia this.
 
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DrSid

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It's just your vision being too slow. And it's not specific to lasers. Lasers are just good at producing fast moving highly visible dot.
 

ARG

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You can take advantage of this effect to make some neat persistence of vision displays :)

 

chipdouglas

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twirling it on a wall and seeing a complete circle is basically the same principle as a projector. its one dot but moving so fast that your eyes cant follow it. no move the twirl super slow, and all you get is a dot going in a circle.

stare at a ceiling fan. looks like a blur. now turn away and quickly look at it, you can, for a brief moment, track one of the blades. Same thing

Michael.
 

FlutterPie

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Like people mentioned above, it's because our eyes are slow. Look at a 60Hz light bulb or monitor. Does it look like a continuous light? Yes

But in reality it is flashing 60 times per second.
 

Eudaimonium

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Like people mentioned above, it's because our eyes are slow. Look at a 60Hz light bulb or monitor. Does it look like a continuous light? Yes

But in reality it is flashing 60 times per second.

Well technically if it were actually flashing 60 times a second, you'd totally notice the flickering.

LCD displays like the one you're viewing now do not "flash" 60 times a second, they only refresh the image on them 60 times a second, while under continuous backlighting to display it.

Ancient CRT monitors had that problem. They were normally at 100Hz rates, with 85Hz being bare minimum if you want to avoid headaches and, presumably, blood squirting out of your eyes.
 
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Well technically, it's called persistence of vision (POV). The chemicals in your retina and neural pathways
all take time to reset. This has been known for many years and is why we can have television and other
scanned displays. If your eyes dart around in a dark room, you will see the individual segments on an
LED clock. Even the old vacuum fluorescent digital clocks did it.
 

Sigurthr

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Also, mains AC powered lamps flash at 120hz (US) or 100Hz (EU), not 60/50 Hz. Each half cycle is a flash.
 




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