Light is a foundational environmental signal influencing plants’ growth, development and life cycles. Photoperiodism is the capacity of a plant to perceive the duration of daylight, enabling it to schedule important biological activities like flowering, dormancy and germination with precision. Photomorphogenesis is the controlled changes in plant structure and development when exposed to light, starting from the emergence of seedlings to the expansion of leaves. The processes above are facilitated by distinct light receptors, such as phytochromes, cryptochromes and phytotropins, which empower plants to perceive various wavelengths and frequencies of light. An analysis of the molecular processes underlying photoperiodism and photomorphogenesis is presented in this chapter, which investigates how plants use light to control both developmental and seasonal responses. Furthermore, it explores the agricultural significance of adjusting light conditions to improve crop yield, especially in controlled environment agriculture. Gaining knowledge about the light reaction of plants enables growers to enhance plant growth and productivity under different environmental conditions.