  By assuming the photosphere located at the outmost edge of the ejecta, Arnett
et al. (1980, 1982, 1989) presented the light curves of homologous explosions
in supernovae analytically and numerically to include recombination effects.
Actually as homologous expansion proceeds, the photosphere recedes deeper into
the ejecta. In this situation, the photosphere radius increases at early times
and decreases later on which can be described by a simple method proposed by
Liu et al. (2018). To study how the photosphere recession effect the luminosity
evolution, we impose a boundary condition on the photosphere to determine the
spatial and time distribution of the temperature of the ejecta which is
clarified to be reasonable. We find that the photosphere recession reduce the
luminosity compared with the previous result without the recession, which can
be tested with observations of Type-IIP supernovae.
