We examine the nature of the opacity and radiation transport in Type Ia sup
ernovae. The dominant opacity arises from line transitions. We discuss the
nature of line opacities and diffusion in expanding media and the appropria
teness of various mean and expansion opacities used in light-curve calculat
ions. Fluorescence is shown to be the dominant physical process governing t
he rate at which energy escapes the supernova. We present a sample light cu
rve that was obtained using a time-dependent solution of the radiative tran
sport equation with a spectral resolution of 80 km s(-1) and employing an L
TE equation of state. The result compares favorably with light curves and s
pectra of typical supernovae and is used to illustrate the physics controll
ing the evolution of the light curve and especially the secondary maxima se
en in infrared photometry.