The photochromic visor automatically darkens depending on the intensity of sunlight (= UV light). This makes both possible to ride in cloudy weather, in bright sunlight and in the dark without changing your visor.
The photochromic reduces 100% of the UV rays that are equally harmful to eyes and skin. This visor makes it kind of a variable sunscreen for the eyes.
How fast this can be done also depends on the temperature, since the warmer it is, the faster the molecules can move and thus change. In good weather it only takes about40 seconds from very clear to a maximum tint.