  We calculate many different nova light curves for a variety of white dwarf
masses and chemical compositions, with the assumption that free-free emission
from optically thin ejecta dominates the continuum flux. We show that all these
light curves are homologous and a universal law can be derived by introducing a
``time scaling factor.'' The template light curve for the universal law has a
slope of the flux, F \propto t^{-1.75}, in the middle part (from ~2 to ~6 mag
below the optical maximum), but it declines more steeply, F \propto t^{-3.5},
in the later part (from ~6 to ~10 mag). This break on the light curve is due to
a quick decrease in the wind mass-loss rate. The nova evolutions are
approximately scaled by the time of break. Once the time of break is
observationally determined, we can derive the various timescales of novae such
as the period of a UV burst phase, the duration of optically thick wind phase,
and the turnoff date of hydrogen shell-burning. We have applied our template
light curve model to the three well-observed novae, V1500 Cyg, V1668 Cyg, and
V1974 Cyg. Our theoretical light curves show excellent agreement with the
optical y and infrared J, H, K light curves. The WD mass is estimated, from the
light curve fitting, to be 1.15 M_\sun for V1500 Cyg, 0.95 ~M_\sun for V1668
Cyg, and 0.95-1.05 M_\sun for V1974 Cyg.
