Hi,
I wiil do some tests with my laserpointers.
1 Can you see the dot, of my 5 mW ,200 mW, and 300 mW green laserpointers, when i point it in the night at a house at 2 and 4 kilometres distance?
Can i and the person standing near his house see the light of the dot?
Thanks.
Remco
REMCO, you do have a thing with brightness.
PLEASE, PLEASE, PLEASE BE EXCEPTIONALLY CAREFUL WITH YOUR LASERPOINTERS, ESPECIALLY THE 200 and 300mw versions!
Okay, some analysis for you, 300MW is about 200 lumens (+0/ - 50). We will use 200 for reference.
I am going to give you the benefit of the doubt and say the beam divergence is 1.5 mrad. Supplier may have quoted less, but I would have my doubts. You can use a beam expander to get this number way down, but that is another topic.
At 2km, you will have a 3 meter diameter spot with an area of about 7 square meters. At 4km, you will have a 6 meter diameter spot with 28 square metre area.
Hence at 2Km, the brightness of the spot is about 30 lux, and at 4km, the brightness of the spot is about 7 lux.
These are of course very approximate estimates.
So what may equate to 30 lux and 7 lux? 30 lux would be a bright street in a highly urban environment. 7 lux would be residential street ... not a dark one, not a light one.
That tells you how bright the spot will be if you are looking at the spot.
How will that appear when you look at the beam directly? The street light analogy is not great here as the candela of a street light varies widely in order to smooth out the level on the street, is relatively low, and the source size of the street light is high. Best example I could give you is take a flash light of about 30 lumens, preferably one with little spill, and shine it on a wall so that the spot is about 1 meter in diameter. Go to that spot and look at the flashlight. This works best with an EDC as the source brightness is generally higher.
I forgot to add, do this last step when your eyes are dark adjusted so you get the full effect.
When the spots go out of your eyes, come back and tell us how bright the flashlight seemed :-)
Semiman
