De-Light: a software tool for the evaluation of direct daylighting illuminances both indoors and outdoors—comparison with Superlite 2.0 and Lumen Micro 7.1

• Published in: Building and environment Vol. 35; no. 4; pp. 281 - 295
• Main Authors: Bellia, L., Cesarano, A., Minichiello, F., Sibilio, S.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.05.2000
• ISSN: 0360-1323; 1873-684X
• DOI: 10.1016/S0360-1323(99)00026-8

Regarding techniques used to evaluate daylighting illuminances, recent years have seen a steady increase in the use of computer programs, owing to increased computer speed and memory capacity. Despite a rise in the amount of available daylighting data, even the latest programs on the market only use standard CIE and IES sky models; besides, input climatic data and calculation procedures used by these programs do not always lend themselves to easy comparison: consequently, in the presence of different results from the programs, it is not always clear which parameters are responsible for these differences. From what has been said above and in order to examine closely various daylighting problems, we can better understand the need to develop a software tool to analyse the influence exerted by the choice of different parameters and calculation models on final results. As regards the various daylighting components (direct-from-sky, direct-from-sun, internally-reflected and externally-reflected), this paper is concerned with the direct-from-sky component, since it is essential for the internally-reflected component calculation. In particular, the procedure which has been developed calculates the direct-from-sky illuminance component on the work plane and on the other interior surfaces that make up the room. Exterior illuminances on unobstructed horizontal and vertical surfaces are also calculated, because they are necessary for the calculation of the externally-reflected component and useful for the reliability evaluation of simplified methods for the calculation of interior illuminances (daylight factor method and lumen input method). The computer program, named De-Light, has been developed in Visual Basic, an object-oriented program language, in order to obtain the greatest flexibility in input and output procedures. In this paper, following a description of the program, we compare the results obtained by De-Light with those obtained by two of the most common and reliable daylighting computer programs, Superlite 2.0 and Lumen Micro 7.1.