  In photosynthetic organisms, the energy of light during illumination is
absorbed by the antenna complexes, which is transmitted by excitons and is
either absorbed by the reaction centers (RCs), which have been closed in this
way, or emitted by fluorescence. The basic components of the dynamics of light
absorption have been integrated into a simple model of exciton migration, which
contains two parameters: the exciton hopping probability and the exciton
lifetime. During continuous radiation with light the fraction of closed RCs,
$x$, continuously increases and at a critical threshold, $x_c$, a percolation
transition takes place. Performing extensive Monte Carlo simulations we study
the properties of the transition in this correlated percolation model. We
measure the spanning probability in the vicinity of $x_c$, as well as the
fractal properties of the critical percolating cluster, both in the bulk and at
the surface.
