It is demonstrated for the first time that photodarkening in colored filter glasses is associated with apparent growth of CdSxSe1−xmicrocrystallites. This is thought to be due to the attraction of impurity ions around the microcrystallites. Both aQ‐switched Nd3+:YAG laser and a hybrid mode‐locked dye laser are used as the light sources. Microcrystallite growth is directly observed by transmission electron microscopy and by field‐emission scanning electron microscopy. Growth is also inferred from local changes in color and measured absorption spectra.