In a book titled Photosynthesis it is easy to forget that light is not simply the energy driving plant metabolism. Light also is the central environmental factor that affects plant size, shape and development. In fact, light activation of photomorphogenic signaling pathways sets the stage for photosynthesis and ensures the maintenance of the apparatus. The effects of specific wavebands of light exert their influence on plant biology from the molecular level all the way up to the higher morphological level, and even contribute to the canopy form as a whole. The wide influence is based on the fact that the light wavelengths that optimally activate photosynthesis also.