Running sunglasses equipped with photochromatic lenses change their tint depending on the luminosity, also protecting the eyes from UV rays. Lenses change depending on the ambient light: they get lighter when the brightness is low and get darker when high . It takes about 10 seconds to get dark. These lenses are essential for athletes who love run in different brightness conditions and different times during the day.
Here is the video tutorial to the photochromic running sunglasses F1000 :