  Starting from the many-body Schr\"odinger equation, we derive a new type of
Lindblad Master equations describing a cyclic exciton/electron dynamics in the
light harvesting complex and the reaction center. These equations resemble the
Master equations for the electric current in mesoscopic systems, and they go
beyond the single-exciton description by accounting for the multi-exciton
states accumulated in the antenna, as well as the charge-separation,
fluorescence and photo-absorption. Although these effects take place on very
different timescales, their inclusion is necessary for a consistent description
of the exciton dynamics. Our approach reproduces both coherent and incoherent
dynamics of exciton motion along the antenna in the presence of vibrational
modes and noise. We applied our results to evaluate energy (exciton) and
fluorescent currents as a function of sunlight intensity.
