irradiation by light (usually visible or ultraviolet) may affect adsorption. In a system containing adsorptive and adsorbent exposure to light may lead to increased adsorption (photoadsorption) or it may lead to desorption of an adsorbate (photodesorption).
PAC, 1976, 46, 71. 'Manual of Symbols and Terminology for Physicochemical Quantities and Units - Appendix II. Definitions, Terminology and Symbols in Colloid and Surface Chemistry. Part II: Heterogeneous Catalysis' on page 77 (https://doi.org/10.1351/pac197646010071)