When driving a load, the photo voltage is variable. As shown in the figure, for a load resistance "R"L, the cell develops a voltage that is between the short-circuit value "V" = 0, "I" = "I"L and the open-circuit value "V"oc, "I" = 0, a value given by Ohm's law "V = I R"L, where the current "I" is the difference between the short-circuit current and current due to forward bias of the junction, as indicated by the equivalent circuit (neglecting the parasitic resistances).