A photochromic lens is a white lens with varying shades: it reacts by adapting to UV and darkens more or less depending on the intensity of the rays. The vision remains comfortable whatever the environment and the wearer is not dazzled. This hue is reversible, that is to say that in the absence of UV, the glass becomes clear again. The advantage is not having to change glasses between the inside and the outside.
It only takes a few seconds for the lenses to reach the maximum category equivalent to standard UV protection (category 3). On the other hand, the time required for the lenses to be completely clear is estimated at a few minutes. The variation in hue is also influenced by the temperature. In cold weather, the lenses darkens quickly, the hue is darker and it takes longer to become clear again. In hot weather, it's the opposite: the lenses darkens more slowly, its hue is lighter and it quickly becomes clear again.
The lifetime of this range of glasses is about 5 years: indeed, the reactions tend to decrease slightly with time and to present a coloring of solar categories 1 minimum and 2 maximum activation.
It should be known that the photochromic lenses cuts 100% of UV, guaranteeing an optimal protection for the eye, whether it is in its activated state or not, ie light or dark. Home windows and car windshields cut off UV rays. As a result, the Signature VII glass we offer does not react and remains relatively clear behind these glass surfaces.
On the other hand, the Xtractive range reacts behind the windshields to a solar category of 2. They darken faster but also take longer to become clear again. Regarding their hue when they are "non-active", they are not totally transparent but retain a slight residual shade of class 0.