The article provides a comprehensive overview of the historical and molecular advancements in understanding how plants perceive and respond to light signals. It traces the research journey from the early 20th century when the USDA began studying the environmental factors affecting crop growth to the present day, focusing on the phytochrome and cryptochrome classes of photosensory receptors. Key milestones include the discovery of phytochromes in the 1960s, the identification of their molecular structure in the 1980s, and the elucidation of their signaling mechanisms in the late 20th and early 21st centuries. The article highlights the role of phytochromes in regulating various plant processes, such as seed germination, seedling development, and flowering, through interactions with transcription factors like PIFs. It also discusses the recent findings on the liquid-liquid phase separation (LLPS) of phytochromes and cryptochromes, which contribute to their signaling functions. The article concludes by detailing the signal transduction mechanisms of cryptochromes, emphasizing their role in regulating gene expression, proteolysis, and other cellular processes in response to blue light.The article provides a comprehensive overview of the historical and molecular advancements in understanding how plants perceive and respond to light signals. It traces the research journey from the early 20th century when the USDA began studying the environmental factors affecting crop growth to the present day, focusing on the phytochrome and cryptochrome classes of photosensory receptors. Key milestones include the discovery of phytochromes in the 1960s, the identification of their molecular structure in the 1980s, and the elucidation of their signaling mechanisms in the late 20th and early 21st centuries. The article highlights the role of phytochromes in regulating various plant processes, such as seed germination, seedling development, and flowering, through interactions with transcription factors like PIFs. It also discusses the recent findings on the liquid-liquid phase separation (LLPS) of phytochromes and cryptochromes, which contribute to their signaling functions. The article concludes by detailing the signal transduction mechanisms of cryptochromes, emphasizing their role in regulating gene expression, proteolysis, and other cellular processes in response to blue light.