The effective and good daylight design has many challenges according to the dynamics nature of daylight. The best way to improve daylight performance is to take a closer look on the behaviour of lighting the interior of sample building spaces. Scale models are commonly used to assess daylighting performance of buildings using an artificial sky for purpose of research and teaching as well as practice. In this paper the daylight assessment performance of the artificial sky at the Stuttgart University of Applied Sciences, Department of Architecture is evaluated. A method was developed, that allows analyzing the main sources of errors by progressive stages. The field measurements were preformed in a South-South-East faced full scale mock-up office. The four photosensors were placed on the middle axis of test office and scale models and the illuminance was measured from these points. The luminance distribution of the sky and the sun at the time of every single measurement was recorded with a luminance camera and fisheye lens. The measurements were done also with three different façade systems which are Venetian blinds with daylight guiding equipment, horizontal louvres and light shelf. This study is an attempt to identify the main sources of experimental errors occurring in the assessment of building daylighting performance by means of scale models. It is aiming to find a correlation between luminance distribution of the sky and outside direct illuminance and internal illuminance levels and describes a strategy for energy efficient lighting design.