Change in the rate of a chemical reaction or its initiation under the action of ultraviolet,
visible or infrared radiation in the presence of a
substance—the photocatalyst—that absorbs light and is involved
in the chemical transformation of the reaction partners.
Source:
PAC, 2007, 79, 293
(Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006))
on page 384