A photograph of the room is shown in Fig. 4, the room is 3.20 m · 2.60 m with a height of 3 m. The test room is equipped with sensors that measure the internal illuminance: a sketch of the test room and of the position of the sensors is presented in Fig. 5. The sensors are indicated through alphabetic letters and through numerical codes (see Fig. 5).
The walls facing north, east and west and the ceiling are prefabricated sandwich panels with a reflectance of 68%; the south-facing wall has a reflectance of 55% while the floor has a reflectance of 45.6%. These values are taken from commercial materials without any particular characteristics and they are not particularly high. Six indoor illuminance sensors (LSI Lastem, Italy) have been used to determine the internal illuminance and an HP data-logger records the measurements every 3 min. The sensors are located on a tripod at a height of 0.80 m that is comparable to a working-plane. The external illuminance has been recorded with an outdoor sensor.