  The main argument against the assumption that quantum fluctuations of the
electromagnetic field are real is that they do not activate photon detectors.
In order to met this objection I study several models of photon counter
compatible with the reality of the fluctuations. The models predict a nonlinear
dependence of the counting rate with the light intensity and the existence of a
nonthermal dark rate, results which might explain the difficulty for performing
loophole-free optical tests of Bell's inequality.
