Background level and counter efficiencies required for a loophole-free Einstein-Podolsky-Rosen experiment

An analysis is made of the background level and counter efficiencies actually necessary to perform a loophole-free Einstein-Podolsky-Rosen experiment. Both requirements are correlated. Photon counters do not absolutely have to have more than 82.8% efficiency if the signal-over-noise ratio is very high.