Re: why are lasers dangerous to eye

From: Don Klipstein (don_at_manx.misty.com)
Date: 01/14/05 

Date: Fri, 14 Jan 2005 14:45:46 +0000 (UTC)

In article <cs8ghs$595$1@informer1.cis.mcmaster.ca>, anton jopko wrote:
>Dear Group,
>Why are lasers dangerous to the eye. Their power is only 5 mw whereas a
>flashlight shining into the eyes would be thousands of times brighter yet no
>one claims flashlights are dangerous to the eyes?

1. A typical 3-D-cell Mag Light may produce about half a watt of
radiation of wavelengths that can reach the retina - but what percentage
would get through your pupil?

2. Once it does get through, it is spread out over a much larger area of
the retina than the tiny point that a laser beam would be focused onto.

3. I figure that Mag Lights and many other flashlights are not so
perfectly safe to stare into for more than several seconds to a minute or
two anyway. (One exposure limit that has regulatory force for laser
products in the USA is 20 joules per steradian in any 10,000 second period
for wavelengths 400-1500 nm, if I remember it correctly. As for steradian
of what - I believe source apparent angular area or retina angular area.)

 - Don Klipstein (don@misty.com)

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