🚀 go-pugleaf

On Wed, 14 Aug 1996 02:03:58 GMT, UZSD78@IBM.RHRZ.Uni-Bonn.DE
(Thorsten Franz) wrote:

>Hello,
>
>when I was sitting in my living room tonight, a spot of red light (at
>most one inch in diameter) appeared on the wall and wandered over it,
>coming to rest on the back of the head of my girlfriend. I wasn't able
>to determine the exact size because it was obviously steered by a
>shaking hand.
>
>I thought it might have to do with a construction site across the
>street and went downstairs to check, but found noone. From down there
>it was clear that the angle wasn't right anyway and that the beam must
>have come from one of the dark windows in a nearby administration
>building, probably 5th or 6th floor.
>
>A laser pointer, as used for presentations on blackboards, would have
>been too unprecise over the estimated distance of 100 meters. I don't
>know of lab lasers with in-built magnifying glasses, and when you play
>with measuring devices you don't aim them at people's head because you
>are probably professional enough to know about the danger of blinding.
>You would also use a stand.
>
>So I figure someone might have been playing with the aiming device of
>a rifle, especially considering how restless the spot was. I will go
>to the police tomorrow and report the scary incident. If anyone can
>give me information that might be useful, confirm my suspicion (so I
>have something at hand when talking to a lazy officer), or calm me
>down, I will certainly appreciate it. :-)
>
>Maybe a physicist can draw conclusions from the estimated distance and
>approximate diameter of the beam, or you know what else portable,
>aimable lasers without a stand/tripod are made for.
>
>Thank you very much,
>kind regards
>
>-- 
>uzsd78@uni-bonn.de
>

If it is the size of 1 inch, you can look into it.
The energy which reaches the retina is small
enough. Then you will know from where it comes.

Do a short calculation:
Original Laser beam diameter = 1 mm
Power in the range 1 to 4 mW usually
Diameter at your window = 25 mm
Intensity per square mm is....
The light has to fill the whole area.

Diameter of eye pupil = 5 mm
how many mW reach the retina?

Red Lasers below 1mW and a diameter of 1mm are
not dangerous, because the eyelid will close
automatically before a damage will occur.
That's why infrared is much
more dangerous.

You can risk a short glimpse.

yours,
wabi


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