Figure 2: Specific growth rate as function of light irradiation plotted as photosynthetically active photon flux density (PFD) for Chlamydomonas reinhardtii; 1000 μE·m−2·s−1 corresponds approximately to 200 W·m−2. The PCE can be read as gradient from the origin to a given point on the curve. Therefore, PCE is at its optimum only in range I, where the circle indicates the point of highest growth rate.