The pigment sensitive for red and far red light is

Photoperiodism is any response of a plant to the relative lengths of daylight and darkness. Initiation of flowering at the shoot apical meristem is one of several physiological activities that are photoperiodic in many plants. The main photoreceptor for photoperiodism and many other light-initiated plant responses (such as germination and seedling establishment) is phytochrome, a family of about five blue-green pigment proteins. It is sensitive to light in the red and far-red region of the visible spectrum.