Most plants reflect green wavelengths while absorbing the rest of the visible light spectrum. In addition, shade plants respond to lower levels of PAR while sun plants harvest PAR more efficiently at higher light levels ⁷. In other words, as solar irradiance (intensity) increases, sun plants experience higher rates of photosynthesis. The leaves of sun plants are small and thick, with special cells allowing for these higher rates ²⁰. Shade plants conduct photosynthesis at a lower radiation intensity level. Their leaves are thinner, longer and contain fewer chlorophyll cells.

Source: http://www.fondriest.com/environmental-measurements/parameters/weather/photosynthetically-active-radiation/