Following an initial experimental study (Thanachareonkit, 2003), which confirmed the larger work plane illuminances and daylight factors observed in a 1:10 scale model in comparison to the corresponding figures in the test module, the main sources of discrepancies were analysed by considering more carefully three different sets of physical parameters : 1) the indoor surfaces reflectance, 2) the scale model outdoor location and 3) the photometers features.

To avoid any bias due to an inadequate mocking-up of the test room, the physical parameters of the 1:10 scale model, comprising geometrical and photometrical features, were reproduced in a very accurate way through an iterative model construction procedure. Table 1 gives the corresponding figures for the test module and the scale model, placed under identical outdoor lighting conditions.

Surface reflectance and workplane illuminance were measured in the test module and in the scale model at the same corresponding height (resp 0.74 m and 74 mm above the floor). An illuminance profile, perpendicular to the single window side, was measured by the way of 6 BEHA photometers placed at 1 m distance each in the test module. An LMT photometer moved by hand in the scale model at the six corresponding positions was used to monitor work plane illuminance in the same way every 15 minutes. Figure 1 shows indoor and outdoor views of the test module and the scale model.

Figure 1: Study process to outline the effect of inaccuracies of the scale model reflectances (a) and location (b).