During the first stages of building design, issues such as local climate, surrounding buildings and orientation are determining factors. The impact of these boundary conditions on daylight illuminances in an open-plan office space is studied in terms of daylight factor, daylight autonomy and useful daylight illuminances. Climate conditions in the location determine the characteristics of the daylight source, such as the ratio between diffuse lighting and global lighting. However, surrounding buildings and elements which may block daylight in the space hold more weight than the orientation of glazed façades, but are not always taken into consideration in daylighting studies.