The experiment on coincidence detection which was done by Grangier in 1986 [18] played a crucial role in rejection of (semi-)classical field models in favour of quantum mechanics (QM). QM predicts that the relative probability of coincidence detection, the degree of second order coherence, g ⁽²⁾(0) is zero (for one photon states), but in (semi-)classical models g ⁽²⁾(0)≥1. We present a purely wave model (based on classical random field) which reproduces quantum probabilities given by the fundamental law of quantum mechanics (Born's rule). The crucial point of our approach is that the presence of a detector's threshold has to be treated not as simply an experimental technicality, but as the basic counterpart of the theoretical model. We call this approach the threshold signal detection model (TSD). In TSD, the degree of second order coherence g ⁽²⁾(0) decreases as 1/Ed2, where Ed is the detection threshold. Hence, by increasing this threshold an experimenter can make g ⁽²⁾(0) essentially less than 1. The TSD-prediction can be tested experimentally in new Grangier type experiments presenting a detailed monitoring of dependence of the degree of second order coherence g ⁽²⁾(0) on the detection threshold.