The discrepancy induced by the use of different photometric sensors in the test module and the scale model was considered as main possible source of error. After an accurate calibration, LMT luxmeters showing a 10 mm diameter sensitive area and BEHA luxmeters, characterized by a 40 mm diameter sensitive area, were compared regarding their cosine response (Schiler, 1987). Illuminances, sensed by the two photometers types for varying incidence angles (0-90 degrees), were measured under a collimated light source, showing spectral features close to daylight (Scartezzini et al, 1994) were measured and compared for that purpose.

RESULTS

The preliminary results achieved within the framework of the initial experimental study, which confirmed the overestimation of daylighting performance assessment in scale models were presented in (Thanachareonkit, 2003). An extended version of this communication will be published shortly, providing a comprehensive and detailed analysis of the impact of the different sources of experimental errors. The present communication is focused on the three main causes of discrepancy between test module and scale model daylighting performance.