Figure 4, curve B shows the cell power (P = EcellI) as a function of I. The maximum power (Pmax) of this photosynthetic bioelectrochemical cell was 0.13 mW (0.29 W m–2 for projective electrode surface area) at R 5 500 V and Ecell 5 0.26 V (I = 0.5 mA). By considering the light intensity (L = 15 W m–2) at our electrochemical cell surface, the efficiency of the light energy conversion (h=Pmax/L) is calculated to be 1.9%