Old 03-29-2012, 06:26 PM #1
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Default Infrared laser safety

Why do infrared lasers pose a threat to your eyes? I understand that since it is invisible, we don't realize how powerful it is, but doesn't it being invisible make it not damaging to our eyes?

What I'm trying to say is, our eye sees the colors we see because it absorbs those colors, just like a green sheet of paper reflects green, but no other colors. I'm curious as to how infrared can be damaging to vision if our eyes don't perceive it.

There most be some limit to which higher wavelengths do no damage right? Like maybe 808nm is bad for the eyes, because it's so close to visible spectrum, but what about (just random) 1400nm?



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Old 03-29-2012, 06:31 PM #2
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Default Re: Infrared laser safety

IR is still absorbed by your eyes. You just can't "see" it as well, as our eyes aren't made to see IR very well.

To most people 808 nm IR appears as a dim red color. Does to me.

It can burn right through dark plastics and dark colored paper, matches light on fire easily, etc.

The back of our eyes is also pretty dark... if focused, yeah, IR is going to do some heavy damage. The real reason people are afraid of IR is mainly because it's almost invisible. You don't know where the dot is going, or how much power it really has; it's really deceiving.
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Old 03-29-2012, 06:31 PM #3
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Default Re: Infrared laser safety

The reason we see visible light isn't that our retinas are able to absorb it, it is that our retinas have chemicals which react to it. Our retinas absorb a very wide spectrum ranging from deep UV to the farthest infrared heat rays (but very far infrared is usually absorbed by the cornea before it gets into the retina).

It is a combination of the thermal energy and the photochemical reaction (destructive bleaching of the eye's pigments) that causes eye damage.

IR is inherently no more dangerous mW to mW than visible, other than IR won't make you blink and you won't know it is happening until too late, but the actual damage mechanism is the same.
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Old 03-29-2012, 06:34 PM #4
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Default Re: Infrared laser safety

It is invisible because we don't have photoreceptors in our eye that respond strongly to IR. That does not mean it is not absorbed.

IR wavelengths close to the visible spectrum like 808nm, for example, is absorbed about as well as 650nm is (by skin). To deeper IR like 10.6um, most materials are opaque including materials that are transparent to visible light. In this case, the damage will not be done to the retina but to the cornea.

The important thing to consider is not only wavelength but also the intensity of the light.

Meh... took too long to post.
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Old 03-29-2012, 07:12 PM #5
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Default Re: Infrared laser safety

If your theory of "Wavelength absorption = damage" is true, then X-rays and Gamma rays would be harmless because most of them just go through us.

But instead, they are really harmful.
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Old 03-29-2012, 07:16 PM #6
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Default Re: Infrared laser safety

Quote:
Originally Posted by Sigurthr View Post
The reason we see visible light isn't that our retinas are able to absorb it, it is that our retinas have chemicals which react to it.
Ah. I did not realize this, though in retrospect, it makes more sense. The reason I was thinking this was because it would be awesome to build a laser only for burning, that can't hurt your eyes at all, and can't be seen. It would look very neat to see a match light on fire for seemingly no reason.
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Old 03-29-2012, 07:30 PM #7
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Default Re: Infrared laser safety

Quote:
Originally Posted by RyanElectro View Post
If your theory of "Wavelength absorption = damage" is true, then X-rays and Gamma rays would be harmless because most of them just go through us.

But instead, they are really harmful.
Those which go through indeed are harmless .. but some of them wont, ant energy they carry is usually pretty high, so even the few does enough mess.

Deep IR (like CO laser) is safer in that respect, that it won't enter the eye. It will be blocked by cornea and lens of the eye, as they are not transparent on these wavelengths. Even if you get direct hit, it will blast front of your eye, but not the insides. And for indirect exposure, it is not more sensitive then rest of the surface of your body.
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