Reconstructing the daylight climatology and the characteristics of the microclimate of a city in a computer simulation environment is not an easy task. Daylighting simulation and analysis of buildings situated in densely built urban environments requires as an input the construction of complex and relative accurate three-dimensional models, which represent real-world scenes.  In order to achieve reliable results in the end of the simulation process, it is crucial for one to identify from the beginning all the factors that could influence the simulation system and consider them as parameters before and during the simulation execution. The paper discusses critical issues in order to achieve higher level of realism in modelling and daylighting prognosis using Radiance.