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The dot

Dubwoofer

New member
Okay so i was wondering, around how many mW whould it take so that if i just lokked at the laser dot pointed at say, a wall, would it take to blind you or cause any damage to the eyes. nm's are 405nm, 532nm, and 605nm.

Edit: ok i just realized i didnt include a surface the surfaces are like a gray carpet and a fence. Like a wood plank fence from like 20ft, and 10ft.

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InfinitusEquitas

Well-known member
No way to answer that question. The answer would depend on the type of material on the wall (how it absorbs and reflects), distance from the wall, the size of the dot, and exposure time.

spyrorocks

New member
Too many variables to consider.

Trevor

Well-known member

Well, let me preface this by saying that you should always wear safety glasses when operating a laser indoors. You'll never encounter a situation as I describe below.

For the purpose of the math, let's assume you have an ideal, 100% reflective matte surface that scatters incident light evenly in a hemisphere radiating from the light source.

First, you want to calculate the area of that hemisphere. Assuming you're about 3m from the laser dot, the area of that hemisphere will be 2*pi*r^2 - 56,548,667.8mm^2.

Next, divide your laser power into that to determine the irradiance per square millimeter. This will be a fairly small number for something like a ~2W laser.

Then multiply that number by the area of the opening your iris allows into your eye to determine what amount of laser radiation would actually reach your eye.

For a 2W laser at a distance of 3m assuming a PERFECT surface, that would be on the order of 0.011mW. If you moved close, like 30cm, that number jumps to over 1mW.

That being said, the hazard doesn't lie in the diffuse scatter - the hazard lies in specular reflections coming from whatever you point the laser at. So disregard the false sense of security gained from pretending there will be ideal conditions with all matte surfaces (no specular reflections or irregular scatter), and just buy some goggles.

Trevor

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InfinitusEquitas

Well-known member

Well, let me preface this by saying that you should always wear safety glasses when operating a laser indoors. You'll never encounter a situation as I describe below.

For the purpose of the math, let's assume you have an ideal, 100% reflective matte surface that scatters incident light evenly in a hemisphere radiating from the light source.

First, you want to calculate the area of that hemisphere. Assuming you're about 3m from the laser dot, the area of that hemisphere will be 2*pi*r^2 - 56,548,667.8mm^2.

Next, divide your laser power into that to determine the irradiance per square millimeter. This will be a fairly small number for something like a ~2W laser.

Then multiply that number by the area of the opening your iris allows into your eye to determine what amount of laser radiation would actually reach your eye.

For a 2W laser at a distance of 3m assuming a PERFECT surface, that would be on the order of 0.011mW. If you moved close, like 30cm, that number jumps to over 1mW.

That being said, the hazard doesn't lie in the diffuse scatter - the hazard lies in specular reflections coming from whatever you point the laser at. So disregard the false sense of security gained from pretending there will be ideal conditions with all matte surfaces (no specular reflections or irregular scatter), and just buy some goggles.

Trevor
Just for emphasis... love that you actually did the math, +3

Having done some testing on a number of surfaces, with a fast response LPM, I'll just second that it's specular reflections you really have to worry about, what's surprising is that so many surfaces can produce them we don't normally consider to be reflective.

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DrSid

New member
If it's not pleasant to look at the dot, and if you have afterimages, then you are getting close.