Photochromic materials change colour when exposed to light and revert to their original colour when the light is removed. These materials can be used to control the intensity of light & to store images, at least temporarily, without chemical development. Furthermore, most photochromics exhibit high resolution capability in image storage.Their main disadvantage is that compared to ordinary photographic films they suffer a low darkening efficiency because they are not chemically developed. Also, many of these materials lose efficiency with use. However, photochromic glasses have several advantages over other photochromic materials simply because they are glasses. By use of standard glass-melting and glass-forming techniques they can be made in any desired size or shape. Their transparency & durability under chemical attack are also advantagous in some applications.
