Abstract: A fast-acting photochromic filter--i.e. a filter whose optical density in the visible light range of 4000 to 7500 angstroms is increased when subject to radiation shorter than 6000 angstroms--which is room temperature stable, that is from at least about 20.degree. to 80.degree.C., consists of (1) a solid optically transparent polymeric matrix, (2) essentially free from non-combined or molecular oxygen, and preferably protected from diffusion of atmospheric oxygen, in which is (3) dispersed, in solid solution, at least one light absorbing compound having a polynuclear conjugated condensed aromatic ring structure, whose molecules are capable of assuming a metastable triplet state by a process of intersystem crossing (not necessarily of the moiety which assumes the metastable triplet state) and in the triplet state, because of closer triplet states, has energy absorption bands whicch occur at lower energies (larger wavelengths) than the singlet-singlet absorption for such molecules.