1. The reduction in photosynthesis caused by exposure to abnormally high intensities of visible or ultraviolet light. Some degree of light-induced damage occurs normally in all photosynthesizing organisms, but repair mechanisms usually ensure that photosynthetic capability is not impaired. Very high light intensity magnifies the damage and can outstrip the repair mechanisms, leading to a decline in photosynthesis, which can be irreversible under extreme conditions. The damage is focused on photosystem II (PSII) in the reaction centres on the thylakoid membranes of the plastids (see photosystems i and ii). During photoinhibition, components of the reaction centre are degraded, causing disassembly of the PSII components. Damaged components are removed, and PSII is reassembled using newly synthesized components.

2. The (usually reversible) suppression of any biological process by exposure to light.