  The feasibility of gamma-ray light sources based on the channeling phenomenon
of ultra-relativistic electrons and positrons in oriented single crystals is
demonstrated by means of rigorous numerical modeling. Case studies presented
refer to 10 GeV $e^{-}/e^{+}$ beams incident on $10^{-1}-10^0$ mm thick diamond
and silicon crystals. It is shown that for moderate values of the beam average
current ($\lesssim 1$ mA) the average photon flux in the energy range
$10^1-10^2$ MeV emitted within the $10^1-10^2$ $\mu$rad cone and 1 \% bandwidth
can be on the level of $10^{12}$ photon/s for electrons and $10^{14}$ photon/s
for positrons. These values are higher than the fluxes available at modern
laser-Compton gamma ray light sources.
