Daylight performance of the Modified Double Light Pipe (MDLP) through yearly experimental tests on a scale model of the system

This work focuses on the Modified Double Light Pipe (MDLP), a daylighting system designed to improve the performance of the Double Light Pipe (DLP). The paper shows the results of a yearly experimental activity carried out on a 1:2 scale model of the device. The dynamic metrics DA, cDA, and U0 have been calculated on a seasonal and yearly basis, and the internal illuminance trend has been determined in four representative days: winter and summer solstices, and spring and autumn equinoxes. The system is effective in delivering daylight in underground areas of buildings both on sunny and cloudy days. Particularly, under overcast sky, a good congruence between internal and external illuminances happens, and linear regression equations allow us to determine the internal illuminance as a function of the external one. Under clear sky with sun, this correlation is less precise at the corners of the room, due to the presence of direct solar radiation, while remaining accurate in the central area. The daylight autonomy is significant for target values of 50 and 100 lx, particularly in spring and summer. DA100 ranges between 0.58 and 0.83 in spring and between 0.66 and 0.83 in summer. The uniformity of daylight distribution on the horizontal work plane can be considered acceptable quite in all climatic conditions, particularly in spring and summer with U0 higher than 0.7 in 81 % (spring) and 85 % (summer) of cases. Altogether, the results can be considered satisfactory.