The regulatory effect of light on plant form, involving the growth, development, and differentiation of cells, tissues, and organs. Morphogenic influences of light on plant form are quite different from the light effects that nourish the plant through photosynthesis because the former usually occur at much lower energy levels than are necessary for photosynthesis. Whereas photosynthetic processes are energy-transducing, converting light energy into chemical energy for running the machinery of the plant, light serves only as a trigger in photomorphogenesis, frequently resulting in energy expenditures that are orders of magnitude larger than the amount required to induce a given response. Photomorphogenic processes determine the nature and direction of a plant's growth and thus play a key role in its ecological adaptations to various environmental changes.