Photochromic glasses are among the most widespread types of glasses, due largely to their popular use in sunglasses. These glasses are used not only in sunglasses, but also in various opto-electronic devices that have been developed and produced throughout the world. Until now, information about photochromic glasses has been widely dispersed in the literature, much of which was published in Russian and therefore of limited accessibility to the Western world. Physics and Chemistry of Photoc...