  We present synthetic bolometric and broad-band UBVRI light curves of SNe Ia,
for four selected 3-D deflagration models of thermonuclear supernovae. The
light curves are computed with the 1-D hydro code STELLA, which models
(multi-group time-dependent) non-equilibrium radiative transfer inside SN
ejecta. Angle-averaged results from 3-D hydrodynamical explosion simulations
with the composition determined in a nucleosynthetic postprocessing step served
as the input to the radiative transfer model. The predicted model UBV light
curves do agree reasonably well with the observed ones for SNe Ia in the range
of low to normal luminosities, although the underlying hydrodynamical explosion
models produced only a modest amount of radioactive Ni56 and relatively low
kinetic energy in the explosion. The evolution of predicted B and V fluxes in
the model with a Ni56 mass of 0.42 M_sun follows the observed decline rate
after the maximum very well, although the behavior of fluxes in other filters
somewhat deviates from observations, and the bolometric decline rate is a bit
slow. Using our models, we check the validity of Arnett's rule and the accuracy
of the procedure for extracting the Ni56 mass from the observed light curves.
We find that the comparison between theoretical light curves and observations
provides a useful tool to validate SN Ia models. The steps necessary to improve
the agreement between theory and observations are set out.
