  We use cosmological simulations to explore the large-scale effects of
reionization. Since reionization is a process that involves a large dynamic
range - from galaxies to rare bright quasars - we need to be able to cover a
significant volume of the universe in our simulation without losing hte
important small scale effects from galaxies. Here we have taken an approach
that uses clumping factors derived from small scale simulations to approximate
the radiative transfer on the sub-cell scales. Using this technique, we can
cover a simulation size up to $1280 h^{-1} Mpc$ with $10 h^{-1} Mpc$ cells.
This allows us to construct synthetic spectra of quasars similar to observed
spectra of SDSS quasars at high reshifts and compare them to the observational
data. These spectra can then be analyzed for HII region sizes, the presence of
the Gunn-Peterson trough and the Lyman-$\alpha$ forest.
