Definition of: photochromism

(fō′tō·krō′miz′əm) noun Physics
The property of changing color under irradiation by the light of a suitable wavelength, the change being reversible by exposure to light of a suitable different wavelength or, in some cases, simply by removal of the stimulating radiation. Also pho′to·chro′ma·tism (-krō′mə·tiz′əm).
—pho′to·chro′mic adjective