  The importance of allowance for the time-dependent effect in the kinetics at
the photospheric phase during a supernova explosion has been confirmed by
several independent research groups. The time-dependent effect provides a
higher degree of hydrogen ionization in comparison with the steady-state
solutions and strengthens the H$\alpha$ line in the resulting simulated
spectrum, with the intensity of the effect increasing with time. However, some
researchers argue that the time-dependent ionization effect is unimportant. Its
allowance leads to an insignificant strengthening of H$\alpha$ in their
modeling only in the first days after explosion. We have demonstrated the
importance of the time-dependent effect with the models of SN 1999em as an
example using the new original LEVELS software package. The role of a number of
factors that can weaken the time-dependent effect has been checked. We have
confirmed that the intensity of the effect is affected by the abundance of
metal admixtures in the envelope, while the addition of extra levels to
themodel hydrogen atom weakens the time-dependent effect to a lesser degree and
never removes it completely.
