**4. Discussion**

The outcomes of the daylight simulations presented in the previous section helped inform the design of a retrofit intervention for a school building that is located in the sunny climate of Sicily (Italy).

Three rooms with different orientation, shape, function, and furniture arrangemen<sup>t</sup> have been considered for designing the most suitable shading and re-directing devices.

What clearly emerges from the analysis of the different metrics is that, if following the current practice of simply complying with the statutory *aDF* and *UR* values, these devices would likely not be installed. In fact, both the standard and computer classrooms show an *aDF* that is lower than 3%, suggesting that more daylight would be desirable, e.g., by installing larger windows. However, the use of the *sDA* and *ASE* metrics suggests that there is already a good daylight availability throughout the year, and, on the other hand, direct sunlight may cause glare issues.

Further analyses that were conducted with the help of the *UDI* metrics allow for binning of the illuminance values achieved on the work plane (i.e., the ideal surface assumed to host the main visual task) under different sky conditions, pointing out that for more than 20% of the occupancy time illuminance seems to be excessive, especially close to the windows. This information is supported by glare calculations that are carried out in terms of instantaneous and yearlong *DGPs* values for observers that are placed in proximity of the windows.

Given the different orientation and amount of glazed surfaces already available, the gym appears the only room complying with the statutory requirements in terms of *aDF* (above 3%) and *UR* values (above 60%). Nonetheless, the high value that is achieved by the *ASE* metrics (almost 70%) suggests considering the implementation of some shading device in order to reduce or completely cut out direct sunlight contribution.

These results consolidate the existing knowledge about the use of CBDM simulations for informing the design process of school buildings [33,34], and further the understanding of dynamic daylight metrics by using a wide range of illuminance- and luminance-based metrics in a comprehensive way. The comparison with the results of traditional and commonly adopted static metrics shows that the messages coming from these static metrics can be deceiving. It is thus reaffirmed that static metrics are not solid enough to support the appraisal of daylight exploitation, at least under mostly sunny and clear sky conditions. Further, it is not possible to use just one metrics (static or dynamic) to judge if and for how long a space is 'well' daylit, but rather different metrics are needed to consider both the spatial and temporal variability of daylight.

What still appears to be critical is the assessment of glare, which depends on several human-related and room-related factors, and how well-established metrics, such as the *DGPs*, could inform the design process. In fact, the calculation of this metrics is strongly dependent on the field of view, so there could be observers suffering from glare for most of the time while others would not. Moreover, as reported by Berardi and Wang in a paper dealing with daylight conditions in an atrium house [35], inconsistencies in the prediction of glare—and of its intensity—should be expected if comparing different glare indexes. When also considering the long simulation times that are required to carry out year *DGPs* calculations (up to four hours for the standard classroom using an i7 2670QM processor), a criterion to carefully select the worst observer's position before running these simulations would be needed.
