Photosynthesis:What is the exact point in time it is initiated? I want to be enlightened as to what is the point in time at any place when green plants initiate the process of photosynthesis? If it starts at dawn, then at what location of the sun below horizen? Another relevant question is whether plants can distinguish between darkness and visible light? If they cant, how the process could be initiated for catching the light? I shall be grateful if guided. Thanks.