photoperiodism
Any process that results in a change in state or activity of an organism (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of detection of, or exposure to, a period of light or dark of a given length, measured relative to a particular duration known as the 'critical day length'. The critical day length varies between species.
GO:0009416
response to light stimulus
is_a
response to day length
exact
response to night length
exact
response to photoperiod
exact