eli5 On projectors, why does the screen show only on the wall, rather than being carried out like a laser?
In: Technology
* You can only see light that enters your eye.
* Everything you see on a projector screen has bounced off the screen and into your eye.
* When you see a laser “in mid air” you’re really seeing the photons of the laser bounce off of something in the air (like dust or haze that has been intentionally pumped into the air).
* The major reason you see this with lasers and not with projectors is:
* Lasers usually are part of a light show, so the whole purpose is to see them in the air.
* For that reason “theatrical haze” is pumped into the air to give the lasers something to bounce of off.
* Also lasers are very focused so there is a lot of photons squeezed into a tiny beam.
* Projectors, on the other hand, are designed to show images clearly on a large screen.
* So they are pointed so that the photos spread out to cover the size of the screen.
* Also in most places where you’d see a projection screen, you wouldn’t use theatrical haze (unless it’s a stage show).
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