photocycle
/ˈfəʊtəʊˌsʌɪkl/Biology and Biochemistry
noun
1A chemical, physiological, or ecological cycle induced by changes in light levels; especially a photoperiodic cycle in plants; a sequence of structural changes that some molecules undergo in response to light.
2A cycle of light and darkness (whether natural or produced experimentally).
Origin
1950s; earliest use found in Proceedings of the National Academy of Sciences of the United States of America. From photo- + cycle.