Re: At what point does one need to protect their e
Remember those little bright and dark spots you see in a room illuminated by a laser?
Those are the places that -- after traveling various distances -- the peaks and valleys of the wave happen to overlap or cancel out.
Any reflective or refractive bending is also going to concentrate the energy.
On the ocean, you get "rogue waves" and with electronics you get "electromagnetic smog" -- points where the energy moving around sums up to a LOT, unpredictably.
You don't want your retina to be focusing any very bright spot, whether it's the direct beam, or a reflection off some flat or curved surface, or the beam refracted through some transparent material -- or even the place where a whole lot of peaks of the wavelength, after traveling various distances, happen to overlap.
From the work on ocean 'rogue waves' here
http://at.yorku.ca/i/a/a/h/51.htm
see this example of waves summing to make a high energy spike
http://at.yorku.ca/i/a/a/h/51.dir/wavetrain.gif