ABSTRACT
Photochromic glasses represent a new class of materials with properties of both optical and photographic media. Common optical and photographic materials are characterized by a number of operational parameters. Devices and units for measuring these parameters have been developed. The main feature of photochromic glasses, variable optical density observed during exposure and upon its cessation, necessitates the creation of special methods for studying and testing those glasses. This feature has to be taken into account for the correct determination of characteristics such as integral and spectral sensitivity, darkening degree and rate, thermal fading, and optical bleaching rates. The structural element of a photochromic material that absorbs actinic radiation, similar to that found in photographic materials, is conventionally called the “center of photosensitivity.” Photometric testing units that provide exposure and probing simultaneously by two different emitters are usually applied to measure the parameters of coloration and fading of photochromic glasses.
