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Our Perception Of Light

God said, “Let there be light, and there was light” (Genesis 1:3); and then Maiman and others came along and made some of it coherent and created a whole new universe of uses for light.  Maiman’s first laser emitted red light, but since that time lasers have been developed which emit a variety of colors.  The average human eye is most sensitive to green wavelengths around 555 nm, and colors appear less bright as they move toward the infrared or ultraviolet wavelengths.  Because of this spectral sensitivity, the beams emitted by green lasers normally appear more visible than those emitted by other lasers, and can usually be seen for long distances, even in a very clean and low humidity atmosphere.  This can be a blessing or a curse.  In many uses, such as some described later, the brilliance of a green beam can obscure the visibility of objects and lights in the vicinity.  In situations where this is a problem, unless there is some overriding reason to use a green laser, it is better to use a laser of another, less visible, color.  Here are some links to better understanding of the physiology of vision and the spectral sensitivity of the human eye: 

http://photo.net/photo/edscott/vis00010.htm
http://www.glenbrook.k12.il.us/gbssci/Phys/Class/light/u12l2b.html
http://hyperphysics.phy-astr.gsu.edu/hbase/vision/bright.html
http://www.rwc.uc.edu/koehler/biophys/6d.html