davidgdg
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- Dec 1, 2008
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In an idle moment I did some calculations on the risk (if any) posed by diffuse reflections.
I got some quite interesting results.
I took as a baseline the risk posed by staring at the sun. A google search suggests there is a risk of retinopathy for exposure of more than about 30-60 seconds. Assuming 1kw per m2 of solar radiation and pupil diameter of 1mm, the sun produces a focused image on the retina with an intensity of about 100 mw per mm2.
Viewing a diffusely reflected spot from a 250mw pointer from a distance of 0.5 metres (a fairly typical eye to match distance for burning!) would produce about the same per mm2 of retina.
Based on this, you would be at some risk of eye damage with the above if you stared at the match-head for more than 20 seconds. A good reason to wear goggles for burning !
On the other hand, diffuse reflections from walls etc pose basically no risk. A diffuse reflection from a 250 mw pointer at 2metres would produce only 6mw per mm2 on the retina which would be unlikely to cause eye damage, even for an exposure of many minutes. Specular (mirror) reflections are of course another matter. Reflections from a powerful pointer may pose a risk of eye damage, depending on the quality of the mirror surface, even at a few metres distant.
I got some quite interesting results.
I took as a baseline the risk posed by staring at the sun. A google search suggests there is a risk of retinopathy for exposure of more than about 30-60 seconds. Assuming 1kw per m2 of solar radiation and pupil diameter of 1mm, the sun produces a focused image on the retina with an intensity of about 100 mw per mm2.
Viewing a diffusely reflected spot from a 250mw pointer from a distance of 0.5 metres (a fairly typical eye to match distance for burning!) would produce about the same per mm2 of retina.
Based on this, you would be at some risk of eye damage with the above if you stared at the match-head for more than 20 seconds. A good reason to wear goggles for burning !
On the other hand, diffuse reflections from walls etc pose basically no risk. A diffuse reflection from a 250 mw pointer at 2metres would produce only 6mw per mm2 on the retina which would be unlikely to cause eye damage, even for an exposure of many minutes. Specular (mirror) reflections are of course another matter. Reflections from a powerful pointer may pose a risk of eye damage, depending on the quality of the mirror surface, even at a few metres distant.
