  We analyze lunar impact flashes recorded by our team during runs in December
2007, 2011, 2013 and 2014. In total, 12 impact flashes with magnitudes ranging
between 7.1 and 9.3 in V band were identified. From these, 9 events could be
linked to the Geminid stream. Using these observations the ratio of luminous
energy emitted in the flashes with respect to the kinetic energy of the
impactors for meteoroids of the Geminid stream is estimated. By making use of
the known Geminids meteoroid flux on Earth we found this ratio to be
2.1x10$^{-3}$ on average. We compare this luminous efficiency with other
estimations derived in the past for other meteoroid streams and also compare it
with other estimations that we present here for the first time by making use of
crater diameter measurements. We think that the luminous efficiency has to be
revised downward, not upward, at least for sporadic impacts. This implies an
increase in the influx of kilogram-sized and larger bodies on Earth that has
been derived thus far through the lunar impact flash monitoring technique.
