650439.fig.001
Figure 1: Phytochrome, cryptochrome, phototropin and the UV-B photoreceptor UVR8 perceive signals of the canopy light environment. The light incident on the canopy has high irradiance, high red/far-red ratio and high blue/green ratio. As light penetrates within the canopy, these values become reduced and the activity of the photoreceptors is also reduced.