Quote:
Originally Posted by Peter Ward
I see what you are saying with regard to power per unit area.....but I suspect there is also the rub...assuming a 100mw beam diverges to say 200mm after a kilometer or so (this approximates my pointer's performance) then the flux in our 1mm beam is being spread over pi*r**2 in area or about 31,000x the area....hence if a
person with say a 6mm pupil is "flashed" we'd have about 5000x less energy going into their eye than say over a few metres...about 0.02 of a milliwatt?
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Hi Peter, and also Nightshift,
a few more rough calculations...
of course the power density (energy per square meter) will fall off hugely as the beam diverges. By the time it has spread out to 200 mm diameter from 1 mm diameter, the energy per unit area will have fallen by a factor of (100X100)/(0.5x0.5) = 40,000, so the 1 mW 1 mm beam will have fallen from an effective 1250 w/m2 to the equivalent of about 40 W/m2.
While will not enough to cause eyesight damage, it will still be very bright - remember that for a laser, the rated power is the radiant output power - not the electrical input power.
A 100 watt incandescent lightbulb is only about 3% efficient, so there is really only about 3 watts of light coming out, the rest is waste heat. So a laser with a diverged 200 mm beam will appear about as bright as a 1300 watt lightbulb at 1 metre...
If you are flying at 10 metres of the ground at 250 knots in a crosswind and in the dark and someone flashes a 1.3 kW lightbulb in your face, you may lose a little bit of concentration as well as some night vision...