## 4 Conclusions  
The CIE Standard General Skies models the SPD of daylight according to the omnidirectional diffuse light reflected and refracted from the entire skydome and not just the highly directional rays from the sun. This standard makes it possible to derive coefficient values directly from measured instantaneous sky illuminance or irradiance or to adjust them independently to simulate and to match any sky conditions. Our benchmarking study reveals the differences in daylight SPDs, with the orientation, altitude and seasonality, on photopic and melanopic estimations, which could potentially modify occupants' responses in outdoor and indoor scenarios. Knowledge of the spectral and spatial patterns of daylight  
Figure 8: CL\({}_{\text{A}}\) values calculated depending on the season (from December 2018 to November 2019); orientation of north (**top**), east (**right**), south (**bottom**), and west (**left**); and elevation from the horizontal level of 15\({}^{\circ}\) (black), 30\({}^{\circ}\) (striped), and 45\({}^{\circ}\) (grey).  
is needed to develop simple outdoor circadian models and procedures to apply them, especially when they should be robust to indoor lighting projects. We have found that based on the CIE recommendations, intercomparison among metrics with high correlation has potential. In addition, the results presented in our study demonstrate that despite the significant variations in daylight SPD in a specific location, it is possible to evaluate the nonvisual potential of daylight based on the analysis of these spectra using the MAF parameter and traditional photopic illuminance.  
In this study, the skies seasonality of Zaragoza during a year in terms of the SPD was studied. Selected clear skies have the highest contribution to both photopic and melanopic illuminances, but data relating to seasonality, sun altitude and glazing orientation in buildings have been measured. The results show that these factors should be considered when outdoor or indoor lighting projects are implemented.  
As a limitation, further long-term SPD measurements are required for the annual study of a specific local daylight contribution. This could contribute to the establishment of general daylight indoor design rules based on real scenarios that consider the total information on the light that exists in the physical environment of each city. Information is lacking on how the daylight SPD may vary depending on geographic location and weather conditions; and another important aspect to consider is that due to the position of the sun vault in the skydome, the SPD is different on different vertical planes depending on both season and orientation. Having access to this information will allow the development of better guidelines not only for interior lighting design but also for the management and control of some biomedical questions such as dermatological [41; 42] and psychiatric pathologies [43] or the improvement of some ocular dysfunctions in the fields of optometry and ophthalmology [44], among others. Finally, it was demonstrated that despite the dynamic variations in daylight and the corresponding variations in circadian values, for each orientation, altitude and season, it is possible to easily calculate a value describing the nonvisual potential of the daylight incidence at the building facade from photopic illuminance and knowing the SPD of the incident light.  
Conceptualization, J.A. and A.S.-C.; methodology, J.A. and A.S.-C.; validation, M.J.L. and I.P.; data curation, S.E. and E.O.-H.; writing--original draft preparation, S.E., E.O.-H. and A.S.-C.; writing--review and editing, J.A., E.O.-H. and A.S.-C. All authors have read and agreed to the published version of the manuscript.  
This research was partially funded by the Spanish Agencia Estatal Investigacion- European Fund for Regional Development, grant number PID2019-107058 RB-I00.  
Not applicable.  
The authors declare no conflict of interest.