The Collaborative International Dictionary of English v.0.48:
Photochemical \Pho`to*chem"ic*al\, a. [Photo- + chemical.] (Chem.) Of or pertaining to chemical changes produced by light; as, the photochemical changes of the visual purple of the retina. [1913 Webster]WordNet (r) 3.0 (2006):
photochemical adj 1: of or relating to or produced by the effects of light on chemical systems