This paper presents a numerical analysis of the daylighting of exemplary office interiors. Simulation results were obtained using a radiance model. The following indexes: UDI, DF, DA, DSP were calculated and analysed for different solutions of building façade. The construction differs in the total thickness of the wall. Two cases were considered: 25 cm and 50 cm opaque sections. Additionally, window magnitude changes from 0.36 m2 to 1.44 m2, with different shapes and locations relative to the centre of the wall. The idea of the work was to find out the architectural solution of the transparent element (geometry and magnitude) taking into account two criteria: decreasing solar heat gains; increasing the daylight utilisation factor. The results are presented in the form of a diagram of daylight distribution as well as average values of visual comfort indexes. The highest values of each indicator (DF, DA and DSP) were obtained for a centrally placed window 1.44 m2. However, the results of useful daylight index UDI depend on the assumed range and it is not easy to identify a relationship between window size and daylight efficiency.