1) Chemical science 2) Chemistry 
• (a.) Of or pertaining to chemical action of light, or produced by it; as, the photochemical changes of the visual purple of the retina.
Refers to the effect of light in causing or modifying chemical reactions. In a photochemical reaction, incident photons are absorbed by reactant molecules to give excited molecules or free radicals, which undergo furthe reaction.
Pho`to·chem'ic·al adjective [ Photo- + chemical .] (Chemistry) Of or pertaining to chemical action of light, or produced by it; as, the photochemical changes of the visual purple of the retina. 
Type: Term Pronunciation: fō′tō-kem′i-kăl Definitions: 1. Denoting chemical changes caused by or involving light.
[adj] - of or relating to or produced by the effects of light on chemical systems
photochemical Referring to the chemical properties of light; chemically reactive in the presence of light or other radiation.
adjective of or relating to or produced by the effects of light on chemical systems
of or relating to or produced by the effects of light on chemical systems