energy in the form of visible ( light ), ultraviolet , or infrared radiation.
Primary photochemical processes occur as an immediate result, and secondary processes may follow. The most important example is {{link=photosynthesis">photosynthesis . Vision depends on photochemical reactions that occur in the eye (see retina ; rhodopsin ). In photographic film and paper, light activates their silver salts to a state that is easy to reduce to metallic silver grains during development. Bleaching of laundry, tanning of human skin, formation of Earth's ozone layer , and many industrial reactions are also photochemical. Certain air pollutants (see smog ) become more reactive and form noxious compounds in photochemical reactions.