Fig. 8

The ratio of specular to diffuse reflections from leaves affects optimal spectral tuning for perceiving leaf-contrast. The optical model revealed that optimal spectral sensitivity for visualizing leaf-contrast depends not only on the specular light source (see Fig. 7a), but also on the ratio of specular to diffuse reflections radiating from the upper leaf surface. This ratio depends on how much of the sky is blocked by overlying canopy. The less light that makes its way through holes in the overlying canopy, the greater the proportion of specular reflections relative to diffuse reflections, and the more beneficial the V-cone for visualizing leaf-contrast. The line at y = 0 indicates the point at which both UV-cone variants see equal contrast