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FrozenGate by Avery

Polarized glasses. Protection?

  • Thread starter Thread starter Deleted member 8382
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Deleted member 8382

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SO the question is if a polarized glasses will protect me against the laser indirect reflections. Those glasses are suposed to block the reflected light so will that happen with laser light too?
 





In a word, no. "Polarized" lenses block light that has certain polarizations. They help block reflected light because reflected light, like off of the surface of water, will have many different polarizations. Since it blocks all but a few polarizations of light, it generally cuts down on glare and reflected rays, but it doens't block all of them.

The glasses, at least the ones I've seen, generally just block all but one orientation of linearly-polarized light, so they would won't completely block light, except for that tiny portion of light that just happened to be at that one orientation that is orthogonal to the polarization that is allowed through. With ALL other orientations, at least a portion of the light would be allowed through.

Polarized glasses are just as useless as any other sunglasses when it comes to laser protection.
 
At best, it will save only one eye with up to an equivalent of OD2 provided the laser is rotated properly.

Indeed "no, in a word"
 
But while I get money for a special googles, will them be better than nothing? Yes, right?
 
Isn't light always polarized horizontally and vertically and nothing more.
And if you put two polarized glasses and hold them like 90 degrees they will block 100% of light any way you hold them, + or x, doesn't matter. So won't one polarized pair of glasses block 50% of the light?
 
Polarized glasses will block light, provided their polarization is rotated exactly 90 degrees from that of the light. For eye protection this is no good at all, reflections are very unlikely to have the exact polarization you expect. Using them may give a false sense of security and hence make things worse.

As for blocking 50% of the light: this is true for light sources with natural polarization (i.e. a combination of random orientations). Sunglasses are usually designed to block horizontally polarized light - i.e. reflections from surfaces like water at a shallow angle.
 
Spoosh said:
Isn't light always polarized horizontally and vertically and nothing more.
And if you put two polarized glasses and hold them like 90 degrees they will block 100% of light any way you hold them, + or x, doesn't matter. So won't one polarized pair of glasses block 50% of the light?
Click to expand...
Light can be polarized in any direction. However, linearly polarized light at and angle can be described by horizontal and vertical components. For example, Linearly polarized light of intensity, I, 45 degrees from horizontal can be described as the sum of the two components I/sqrt(2) horizontal + I/sqrt(2) vertical. More generally with incident linearly polarized light at angle, a, and intensity, I, the transmitted light through the polarizer is I*(cos(a))^2. Regular 'unpolarized' light is thought to have polarized components in all directions. This unpolarized light is cut in half when transmitted through a linear polarizer.

Additionally, most sunglasses are not ideal polarizers and don't block all the light that they would in theory. You can see this if you take two lenses and hold them perpendicular to each other. Looking close it's easy to see that light is still getting through at the position where it is darkest.
 
ONLY LASER SAFETY GOGGLES ARE LASER SAFETY GOGGLES. THINGS WHICH ARE NOT LASER SAFETY GOGGLES ARE NOT LASER SAFETY GOGGLES.

Come on people, it's your eyes we're talking about.
 
They are a 130$ polaroid glasses. DOn't know if they pass any standart but they were the best on the shop when my father bought them long ago.
 
--Hallucynogenyc-- said:
They are a 130$ polaroid glasses. DOn't know if they pass any standart but they were the best on the shop when my father bought them long ago.
Click to expand...


You've gotten your answer several times now. Sunglasses are not laser goggles and shouldn't be used as such

They do reduce incoming light but not enough to be safe for your eyes, they also make the pupils dilate which puts you at even more risk.
 
Why bother posting a question if you're not going to listen to the answers? Several people who have answered you here are laser professionals, we do this for a living... why would we mislead you about safety?
 
well the fact is that I'm not asking for the ultimate solution, just if this is better than nothing. Ofc sunglasses are worse cuz of dilatation etc, but I've been told now taht it can filter 50% of a reflected light while others say they don't.

I'm not asking bout normal sunglasses, I'm asking about polarized!
 
Let me explain to you what polarization is.  Light waves are a wave in the sense that they can move either up and down, or left and right.
http://en.wikipedia.org/wiki/Polarization
Here is a good diagram:
polariza.gif


Now, normal sources of light such as a light bulb have random polarization (Aka light comes out at every angle).
Lasers are polarized (Every photon is polarized the same).

A polarizing pair of sunglasses will block horizontally polarized light and pass vertically polarized light, the reason why this blocks reflections in real life is rather complicated; however, light has a higher chance to bounce when its axis of polarization is perpendicular to the surface normal.

Try an experiment, take a cheap 5mw red laser and shine it through your polarizing glasses.  Spin the laser and you will see that at some angles all of the light gets through while at other angles half or so may be blocked.

Basically this means that your polarizing glasses may protect you very slightly half the time, and the other half of the time you are going to get the full laser right in your eye (except worse because your eye is dilated). It all depends on how you are holding the laser.  I would consider this to be far worse than having no protection at all. You are giving yourself a false sense of security while making it more likely that a hit with the laser will cause damage.
 
Light polarization is also much more complicated than just "some is vertical and some is horizontal". Linear polarization like that is a simple case of general polarization, which is elliptical.

Again, no, it's not ANY better than regular sunglasses for a laser. You have no way to know what polarization of light is coming at your eye, so you have no way of knowing how much of that light will get through. Sure, there's a chance you may block some percentage of that light by the fact that it's polarized. But there's also a chance that the polarizing filter could be allowing 100% of that light through. They don't just "filter 50% all the time", the amount filtered depends on many things, none of which you can control.

The simplest, purest case is a single, linear polarization of light coming in. In that case, you have equal chances of having all the light come through as having none of the light come through, and it could be anywhere between those 2 conditions. But it's never that simple, it's MUCH more complicated than that, and none of the complications help your chances, they only hurt your chances.

Seriously, it's not any better. Please go learn what polarized means, and what polarizing filters actually do. It's not ANY better than any regular sunglasses.
 
--Hallucynogenyc-- said:
well the fact is that I'm not asking for the ultimate solution, just if this  is better than nothing. Ofc sunglasses are worse cuz of dilatation etc, but I've been told now taht it can filter 50% of a reflected light while others say they don't.

I'm not asking bout normal sunglasses, I'm asking about polarized!
Click to expand...

Yeah... don't listen to the members that posted.... what do they know... :P

Yeah... your right.... it's better to go partially blind than completely blind... :'(

"Yeah... that's the ticket" ::) ::) ::)

Oh... BTW.... they are not my eyes...........................  8-)

We use Laser safety Goggles...
I believe we have we have 4 different pairs to cover the lasers
we use in the shop....

Jerry
 
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