What are photoperiods?
The time that a plant or animal is exposed to light in a 24-hour period is called as its photoperiod.
Photoperiod is also called as light duration and day length. Plants require particular time period of light exposure to enter various life cycle stages. Day lengths control or influence several plant growth and development processes that determine or affect crop yield. According to their requirement of light periods, plants may be considered as short day plants and long day plants.
Photoperiodism is a related term and refers to the physiological reaction of organisms to the length of day and night. It occurs in plants as well as animals.