I did some careful controlled experiments after I aquired my 1st two hipower lasers recently. I figured it was best to know and find out from careful deliberation, rather than from an accident later.
Have to refute what's been said about red lasers a little...
My 200mw green Gatlin causes a "sting" on my forearm and on the back of my hand, when it's *FOCUSED*, at a short distance of 8 to 12 inches or so. The pain is high enough so that I have to stop it. From a distance of ~ 20 to 30 feet, when focused at infinity ("infinity" = a target ~ 260 meters away), I get a warm sensation after about 10 seconds or so. It's tolerable, and doesn't seem to "build up".
For my Survival Lasers 660nm Red, rated at 300mw; I replaced the default acrylic lens with a jayrob 650-G-1 lens, so now it is probably putting out ~ 370-380 mw.
At close distances and focused, the 660nm DEFINITELY hurts within a very short time, both with the old and the new lens.
When focused at infinity; from 20-30 feet away, I get a "hot" sensation that can be tolerated, for a little while.
I have definitely noticed an improvement in burning capability after switching to the G-1 lens for the 660nm.
I am "average/fair" skinned, but spent years in the tropics in different places. There is a "hint" of "weathering", a "hint" of a "residual tan".
Maybe my blood just moves slower than average? I *DO* have a damaged heart, and occasionally *DO* take nitroglycerin for angina, and take aspirin daily. Maybe that has an effect on tissue cooling. I've developed a low tolerance for heat in the past few years.