  Neutrinos are copiously emitted by neutron star mergers, due to the high
temperatures reached by dense matter during the merger and its aftermath.
Neutrinos influence the merger dynamics and shape the properties of the ejecta,
including the resulting $r$-process nucleosynthesis and kilonova emission. In
this work, we analyze neutrino emission from a large sample of merger radiation
hydrodynamics simulations in Numerical Relativity, covering a broad range of
initial masses, nuclear equation of state and viscosity treatments. We extract
neutrino luminosities and mean energies, and compute quantities of interest
such as the peak values, peak broadnesses, time averages and decrease time
scales. We provide a systematic description of such quantities, including their
dependence on the initial parameters of the system. We find that for equal-mass
systems the total neutrino luminosity (several $10^{53}{\rm erg~s^{-1}}$)
decreases for increasing reduced tidal deformability, as a consequence of the
less violent merger dynamics. Similarly, tidal disruption in asymmetric mergers
leads to systematically smaller luminosities. Peak luminosities can be twice as
large as the average ones. Electron antineutrino luminosities dominate
(initially by a factor of 2-3) over electron neutrino ones, while electron
neutrinos and heavy flavour neutrinos have similar luminosities. Mean energies
are nearly constant in time and independent on the binary parameters. Their
values reflect the different decoupling temperature inside the merger remnant.
Despite present uncertainties in neutrino modelling, our results provide a
broad and physically grounded characterization of neutrino emission, and they
can serve as a reference point to develop more sophisticated neutrino transport
schemes.
