In 1948, spectrograph tests indicated that a single pigment was responsible for the photoperiodis. In 1952, tests revealed that germination was stopped when a plant was exposed to far­red light and restarted when exposed to red light. In 1959, the team performed conclusive tests on turnip seeds and named the pigment phytochrome. 

Photoperiod is the duration of sunlight received by any place.It affects the natural vegetation of any place. The photoperiod is different at different places because of the variations in latitude, altitude, season and duration of the day