  We present theoretical UBVI- and bolometric light curves of SNe Ia for
several explosion models, computed with our multi-group radiation hydro code.
We employ our new corrected treatment for line opacity in the expanding medium.
The results are compared with observed light curves. Our goal is to find the
most viable thermonuclear SN model that gives good fits not only to a typical
SN Ia light curves, but also to X-ray observations of young SN Ia remnants. It
appears that classical 1D SN Ia models, such as deflagration model W7 and
delayed detonation one DD4, fit the light curves not so good as a new 3D
deflagration model by Reinecke et al. (which is averaged over angles for our LC
modelling). This model seems good also in reproducing X-ray observations of
Tycho SNR. We believe that the main feature of this model which allows us to
get correct radiation during the first month, as well as after a few hundred
years, when an SNR forms, is strong mixing that pushes material enriched in
iron and nickel to the outermost layers of SN ejecta.
