Photochromic lenses in use ordinary consumers called chameleons. The name explains the essence of the work of photochromic lenses. Points such lenses under the influence of sunlight dimming, with a decrease in the intensity of the sun shade also reduced.
I would like to note at once that, as photochromic lenses configured to darkening under the influence of UV light, you can not use these glasses for driving. Because UV does not pass through the car glass, so the whole effect of darkening of photochromic lenses is lost.
As a similar effect is achieved with glasses-dimming Chameleon?!
The basis is photochromism sensitivity to light of certain substances, more precisely - to electromagnetic radiation of a certain wavelength, which causes discoloration; in the absence of the activating radiation is returned to its original state. The reverse process is initiated in the photochromic substances temperature and visible light. In essence photochromic conversion process is as follows. Chemical X is excited by ultraviolet radiation and becomes Y substance which has a specific absorbance. If exposure to ultraviolet radiation is stopped, the substance Y goes back into a colorless substance X.
In mineral photochromic lenses in photochromic pigments are used as silver and copper halides. The organic photochromic lenses used three groups of photochromic organic compounds, oxazines (oxazine), derivatives fulgides (fulgide derivatives) and naphthopyrans (naphtopyran). Photochromic pigments of different groups differ from each other in structure, size, color in the activated state, as well as sensitivity to temperature and ultraviolet. Oxazines are characterized by high rates of activation / deactivation, they are resistant to photodegradation by UV-radiation and therefore longer retain photochromic properties. However, they are sensitive to temperature, so bad manifest themselves in countries with hot climates. Derivative fulgides have good speed activation / deactivation, but for fatigue index (the number of dimming / brightening cycles) they are inferior to the other photochromic pigments. Naphthopyran compounds of the groups have a balanced set of properties, thus less dependent on the temperature.
Modern organic photochromic lens containing photochromic pigments of the three types, and each of the organic photochromic lens manufacturer has its own formulations photochromic components.