(of chemically treated glass or plastic) capable of darkening or changing color when exposed to light.
Origin of photochromic
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
(of glass) changing colour with the intensity of incident light, used, for example, in sunglasses that darken as the sunlight becomes brighter
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012