  Observation of the expansion history of the Universe allows exploration of
the physical properties and energy density of the Universe's various
constituents. Standardizable candles such as Type Ia supernovae remain one of
the most promising and robust tools in this endeavor, by allowing for a direct
measure of the luminosity distance-redshift curve, and thereby producing
detailed studies of the dark energy responsible for the Universe's currently
accelerating expansion. As such observations are pushed to higher redshifts,
the observed flux is increasingly affected by gravitational lensing
magnification due to intervening structure along the line-of-sight. We simulate
and analyze the non-Gaussian probability distribution function of
de/amplification due to lensing of standard candles, quantify the effect of a
convolution over many independent sources (which acts to restore the intrinsic
average (unlensed) luminosity due to flux conservation), and compute the
additional uncertainty due to lensing on derived cosmological parameters. For
example, the ``degradation factor'' due to lensing is a factor of three
reduction in the effective number of usable supernovae at z=1.5 (for sources
with intrinsic flux dispersion of 10%). We also derive a useful expression for
the effective increased dispersion in standard candles due to lensing, as a
function of redshift.
