One of the most important effect in the losses of photovoltaic modules is the sharp drop in conversion efficiency at low light level. Actually, modules efficiency decreases differently depending on the PV technology, usually when the light goes below 200 W.m-2. This phenomenon cannot be observed in standard test conditions because the light is fixed at 1000 W.m-2. This paper provides a technique to take into account the low light conversion efficiency of modules using outdoor characterizations during few weeks. It also shows methods to determine more precisely that effect in models that predict PV producible (PVsyst, Sandia model...).