The use of lasers in airsoft is surrounded by controversy and contradictory information. I have spoken on lasers on CQB Radio, Episode 12.

http://cqbradio.blogspot.com/2010_02_01_archive.html

Most laser sights are under 5mW in power.  This can injur the eye with prolonged exposure, but the human eye has a protective reflex when exposed to such bright lights.  You naturally blinik or look away before much damage can be done.  There are class 2/II lasers which are used in laser pointers and low-power gun sights which would not be expected to cause accidental injury.  I wish all laser sights used in airsoft were limited to class 2 (or class II).  Many real steel sights are class IIIa or class 3R which means up to 5 mW.  This is unecessary in the distances involved in airsoft and there is minor risk of accidental injury.  It really takes purposely staring into the light to cause a significant effect on vision.  The effects of accidental exposure to under 5 mW of energy rarely if ever result in permanent injury.

I have yet to find data in the medical literature which supports the idea that green lasers are more harmful than red.  It would be safe to avoid class III/3R green lasers.  You should be fine with any color of class II/2 laser.  Use caution with class III/3R lasers and never look at them through a magnifying scope.  The scope can magnify the light and increase the damage done by a low-power laser.

II encourage airsoft retailers to prominently display "Class 2" or the power rating in milliwatts on appropriate laser sights that are low powered so that we can feel safe playing with them. I would feel completely comfortable playing against other players using "Class 2" lasers.

Dr. Airsoft Recommendation: Use and play only with Class 2 and Class II (<1mw) lasers

Online Retailers Carrying Class II or Class 2 laser sights: