Abstract
The two best-known photophysiological processes are photosynthesis and vision. In photosynthesis light energy is absorbed and transformed into ‘life energy’, in vision the information content of light is utilized by organsims. In photosynthesis chlorophyll and other pigments involved in light-gathering are not chemically changed (except that some of the chlorophyll or phaeophytin molecules are oxidized and immediately reduced again). In human vision the rhodopsin and other visual pigments undergo a reaction cycle induced by photon absorption. The pigment is brought back to its original state only after a long chain of chemical reactions.