Part of the definition of a class IV laser, says that specular reflections become MORE of a hazard. Its not like you cross the 500mw line and then BAM!! The dot becomes damaging to look at. There are a BOAT load of factors that go into this, the laser wavelength, the optical density, the reflection spectrum of the surface being hit, and the distance the viewer is from the dot.... are a few to name.
Lots of Math.
To put it simply, Class IIIa can cause damage from a direct hit if the direct hit is sustained for longer than about .25 seconds, or longer than the eye has time to blink. And I mean damage, by ANYTHING that happens to the eye, whether un-noticeable, minor, or permanent.
Class IIIb can cause damage in LESS than a quarter of a second from a direct hit.
Class IV can cause damage from the coherent light that is reflected off a surface that is not normally very reflective... like a white wall.
The factors I mentioned earlier, such as distance from the dot, can EASILY turn a class IIIb laser into a class IV.
If you are looking at the dot of a 100mw laser from 1 decimeter away... you CAN be susceptible to damage like a class IV could give from 2 decimeters, to 15 meters away. It all depends on your setup.
This means, just be safe, use your brain, and don't think twice about something, just go the extra mile JUST IN CASE.
I would say that viewing a 200mw dot from a white wall should be safe without glasses if the distance between you and the dot is controlled, the laser has been secured and power regulated to reasonable degree, and access to the beam is controlled. But this is what I would say, feel free to go the extra two miles.
The less you can change ANY variable during a viewing situation, the better.
Be safe!
-Tyler
. so i guess for that I'll only use with glasses unless outdoors and pointing at mountains or whatever.
