The sensitivity of the human eye peaks at about the same wavelength as the green light in the color spectrum. As such, given red and green laser lights both having 1 mW power output, the green laser light will come out 30 times brighter than the red light. Greenlight also tends to scatter more than red light so the beam can travel greater distances than a red beam. In simple words, green lasers are brighter and are more visible over longer distances than red lasers even without the aid of laser detectors. Because of this, green lasers are costlier, too.