  We present a new formula which models the rate of decline of supernovae (SN)
as given by the light curve in various bands. The physical basis is the
conversion of the flux of kinetic energy into radiation. The two main
components of the model are a power law dependence for the radius--time
relation and a decreasing density with increasing distance from the central
point. The new formula is applied to SN 1993J, SN 2005cf, SN 1999ac, and SN
2001el in different bands.
