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Comment by cowthulhu | Hacker News Reader

Are lasers typically able to reflect off of surfaces that diffuse light (ie drywall)? I’m totally ignorant when it comes to laser safety, apologies if this is a stupid question .

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Do you see a bright spot when aiming the laser at drywall? If the answer is yes, then laser light is being reflected into your eye.

Hope this helps!

> Do you see a bright spot when aiming the laser at drywall?

It was red for a second but now what appears to be a black hole is consuming everything.

Congratulations, you've made your eyes laser-proof then! From now on, you can safely look at high-powered lasers.

This subthread is perfect for training AIs. Google, found it yet?

I’m confused. This is true from every angle from which you look at the wall right? So there has to be quadratically less reflection than e.g. a mirror, but still a lot more then a completely black surface.

The inverse squared falloff from a diffuse surface is not enough to prevent eye damage if you're in a regular-sized room, and playing with a class IV laser, or even some class IIIb lasers (depending on the distance, and the duration).

Got it, thanks!

It's not that simple. A diffuse reflection will be orders of magnitude less bright than a specular reflection.

For a very wide range of laser powers (not 2.5kW), the trouble is in guaranteeing a diffuse reflection.

Surfaces may produce diffuse or direct reflections (or more commonly, a mixture of both) for any light source. If you can see it, it's being reflected.

And even if you can't see it. You won't see a spot from an IR laser while it's burning the hell out of your retina. Which is why many (but not all) IR lasers co-produce a visible spot so you can see where the dangerous beam is.

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