For your first question the NOHD usually varies depending on the wavelength as the more visible a beam is, the more hazardous it is to the eyes without staring into the diode. You can have a 50mw 445nm and a 40mw 520nm and the 520nm will be more dangerous as it is higher on the visible spectrum.
This is incorrect.
Green is not more "dangerous" than other wavelengths. Green looks brighter because the photoreceptors in your eyes respond to it more strongly than to other wavelengths, not because green is somehow "more powerful". In fact, green is actually LESS dangerous than other colors, because the strong photoreceptor response triggers your iris, blink, and general aversion reflexes at a lower level of power.
Compare, say, 532nm (green) and 405nm (violet), aimed at a white wall, 10 feet or so away. 500mW in each case. The green dot is going to look brilliantly, painfully bright. You won't enjoy looking directly at it for long. But the violet dot probably won't cause you any discomfort at all, even if you look at it for minutes on end. Both lasers are 500mW, however, and both will do the same amount of damage to your eyes.
Now throw a couple NIR's out there too, 808nm and 980nm. At 500mW the 808nm will be barely visible at all, maybe a dull purple-red dot, no visible beam. The 980nm will be totally invisible and your eyes will not react to it at all. Both of them will do the same damage as the green and violet, because they are 500mW, and on a direct hit, damage is determined by power, not wavelength.
There is another danger to consider as well: It's easy to forget that the 405nm is 500mW, because it's so dim. Violet lasers all tend to look alike, even comparing lower power vs high. A 500mW violet isn't *that* much brighter than an 80mW ebay violet, despite being more than 6 times as powerful. With infrared lasers it's even worse because on top of this, things like reflection hazards become a lot harder to avoid.
The green, on the other hand, is so bright at 500mW that it hurts your eyes just looking at the dot, so you KNOW it's nothing to mess around with - and that makes you act more carefully.
In other words - on a direct hit, power is dangerous, not wavelength. In terms of psychology and your eye's (lack of) response, less-visible wavelengths are more dangerous than highly-visible ones, because your aversion doesn't kick in, which can lead to complacency and carelessness, IF you allow that to happen.
THIS stuff is what I mean by knowing basic facts and whatnot....
ETA:
nightwalker said:
Im not a pro in this field but i still know about laser basic concepts...maybe sending me a link of choosing a laser pointer would be good for me
Tell me about wavelength again?
This is the kind of think-you-know-it-all attitude that gets people injured and into trouble. Sorry I can't help.