This cheap 400mW green laser pen is an extremely powerful laser, the beam is very visible at day or night, which is a very suitable equipment for outdoor sports enthusiasts. It is recommended to use an astronomical point to the starry skies or amaze your friends.To work, this high quality green laser pen 400mw requires the use of 2 AAA batteries.This green laser pen has a wavelength of 532nm which gives a particularly intense green (650 nm against a red and 405 nm for blue), this 532nm wavelength light is the most visible to the human eye.