To conduct the study on the natural lighting the software package ADELINE [10] has been used. This software package has been developed by a department being part of the Organisation for Economic Cooperation and Development (OECD): the International Energy Agency (IEA). One of the main IEA’s goals, within the programme "Solar Heating & Cooling” (Task 21), consists in the development of the natural lighting technology by favouring an innovative and self-conscious lighting design. ADELINE (acronym of Advanced Day and Electric Lighting Integrated New Environment) is a sophisticated integrated software tool for lighting design being able to work out, by the analysis of a wide range of inputs (geometric, photometric, climatic, optical data etc.), realistic simulations, graphic and numerical information [10].

Inside ADELINE, a CAD program, Scribe Modeller, allows modelling the room being studied and is connected with two very well known lighting calculation programs, Superlite and Radiance, by a conversion program, Plink, allowing to simplify the complex input deriving from Scribe. The tridimensional outline of the studied object could be also realized using other CAD systems, availing theirselves of a further conversion program included in the package, but the restrictions imposed by Superlite [10] generally do not allow to use the model such as it is worked out by the widespread CaD programs; from this it follows that the modeller Scribe, even though it is quite primitive compared to the commonly used design software tools, turns out to be much more easy to use.

The study module on which the lighting analysis has been performed is represented by one of the two side bays of the central body; this module consists of one of the four lecture halls, while, according to the state of the project, it consists of a side bay of the new reading room. The modelling performed with Scribe has met with most serious difficulties in the definition of the vaulted roof as Superlite does not import curved lines and surfaces. For this reason the vault straight arch has been schematized with a broken line, and the vault itself with inclined planes, the realization of which passes through a very complex process. The lantern has been simulated with a parallelepiped having glazed side faces and opaque upper face, while the lower face, leaned on the horizontal plane delimiting the top of the vault, is schematized with a glass having a transmission coefficient of 1.0, like an open space. For the simulation of the surroundings two obstructions have been introduced: the first, on the west side, simulates the presence of the pavilion “C”, situated at a distance of about 14 m, the second, on the east side, simulates the presence of the medieval walls being about 1.50 m far.

The glazed surfaces (i. e. the two portals on the west facade, the lantern windows and the new large glass facade towards the medieval walls) have been schematized with a plain glass having a transmission coefficient of 0.90. The opaque enveloping surfaces are characterized by opportune reflection coefficients according to the material and to their scheduled dye: for the walls a reflection coefficient of 0.60, corresponding to mean-light dyeings has been considered, while a reflection of 0.30, corresponding to dark dyes, and a coefficient of 0.85, corresponding to very light colours, have been considered, respectively, for the floor and for the vault intrados. Finally, the two work planes have been intoduced according to which the values of illuminance and of daylight factor inside the study-module are calculated; they correspond to the new library reading desks: the first, placed at the height of +0,80 m and the second at the height of +4,20 m, coinciding with the reading work plane on the mezzanine floor.

Once the tridimensional model has been realized and imported, by Plink, into Superlite, it is possible to carry on the lighting simulations. This program requires as an input, in addition to the geometrical model, the definition of the site and of the sky models. Three possible ways exist for the site definition: assigning the position of the sun and the site radiance data, assigning the site geographical data as well as the atmospheric ones relating to the air turbidity and, finally, assigning the position of the sun and the data on the air turbidity. The first of the three options has been necessarily chosen, since systematical data on the air turbidity all over the national territory are not available [11-12]. The site identification (Pisa, Tuscany region) has, therefore, occurred by the definition of the sun position (altitude and azimuth angles, variable with the simulation day and hour), of the altitude compared to mean sea level of the site of interest (4 m, in the case investigated), of the ground reflection coefficient around the building (asphalt: reflection coefficient of 0.07) and of the data relating to the site radiance, in particular the values of the direct solar radiation as well as of that diffused by the sky onto a horizontal plane and, finally, the relative luminous efficacy, constant with the variation of the simulation day and hour, and assumed to be equal to 105 for the direct value and 140 for the diffused value [13-14].

The sky models contemplated within the package ADELINE coincide with the models standardized by the Commission International de l’Eclairage (CIE), that is the model: CIE Standard Overcast Sky (defined as a completely overcast sky in which the sun position cannot be seen, and producing, on a horizontal plane without obstructions, a illuminance of 21500 lux) and CIE Clear Sky with Sun (defined as a sky covered with clouds for less of the 30% of its apparent surface). It has to be remembered that such standardizations, occurred around the 50s, refer to two extremal meteorological conditions and recent studies have demonstrated their inadequacy especially in certain climatic regions [15]. In fact new models, representing intermediate conditions compared to those described in the models CIE (it is the case of the sky model “Mediterranean”, representative of the illuminance conditions at our latitudes), have been recently elaborated [16].

Once the required inputs have been introduced, Superlite calculates the illuminance on the work planes existing in the tridimensional model. The results are described numerically in terms of illuminance level or daylight mean factor and visualised with isolux curves.