Kestrel Pocket Weather Meters is excited to announce the release of the Kestrel 4000 NV! This great unit continues to bring you all the functions and reliability you`ve come to expect from Kestrel with just a little something more. The NV`s red backlight preserves the natural night vision of users such as military personnel and pilots. It takes 30 to 45 minutes for the average eye to adapt to darkness and maximize night vision. Even a short burst of white, yellow, green or blue light "bleaches out" the rod cell photoreceptors in the eye and causes night blindness until the entire adaptation process can take place again. Light in the red spectrum does not cause this "bleaching out", preventing night blindness and night vision fatigue.