## 5 Experimental Characterization of the VSC in Burgos  
The experimental values of the VSC calculated from Equation (6) were obtained for the city of Burgos. Figure 6 shows the VSC values, classified by intervals, and for the four vertical cardinal orientations. As can be seen from Figure 6, VSC values lower than 20% were practically nonexistent on surfaces facing the four cardinal orientations. VSC values within the interval between 20% and 40% had high FOC, ranging between 6.74% (south-facing surface) and 52.53% (north-facing surface). The following VSC interval, from 40% to 60%, presented FOC of almost 30% in all four cardinal orientations. VSC values between 60% and 80% could also be found in all cardinal orientations with FOC of 23.4% for south-facing facades and 10.91% and 10.16% for east- and north-facing facades, respectively. VSC values higher than 100% were present in all directions, with greater frequency on the south- (21.94%) and the east-facing surfaces (33.68%). Building design must take into account the availability of daylighting for proper building and room design factors, such as depth, floor area, glazing surface, and window heights and widths, among others. High VSC values usually result in a greater illumination in interior spaces. Different buildings standards [43; 44; 45] establish minimum levels of VSC for more effective daylighting [46]. If the obstruction angle of external obstructions is no higher than 25\({}^{\circ}\) above the horizon, then VSC values \(>\)27% usually indicate good daylight availability [14]. It must be noted that the VSC target value of 27% is a figure based on low-density suburban housing models. The daylight and sunlight review states that in an inner-city urban environment, VSC values in excess of 20% should be considered as reasonably good. However, whenever the VSC value falls below 10%, then the availability of direct light from the sky will be poor. As pointed out in Figure 6, high VSC values are predominant in Burgos in all cardinal orientations. Table 7 shows the frequency of occurrence of VSC values higher than 27% for surfaces facing the four cardinal orientations. This study, therefore, shows that the availability of daylight in Burgos is very favorable for integration into the lighting design of buildings. Detailed plans for new city developments accept higher urban density, thereby increasing the difficulties associated with the required levels of daylight. The impact of site layout on daylight conditions, especially in dense urban areas at high latitudes, has been remarked upon by several authors [47]. High VSC levels mean that even dense urban areas can have good daylighting conditions. Figure 6: Distribution of VSC values by intervals calculated in Burgos, Spain, between September 2016 and January 2019. A seasonal study of Burgos VSC conditions was completed using the CIE standard classification for homogeneous skies. Knowledge of the sky type permits the determination of VSC on any surface regardless of its orientation, due to the univocal relationship between the sky type and the illuminance distribution. This approach presents the advantage that CIE standard classification can be done using different procedures that avoid the use of sky scanner devices [32]. Firstly, the seasonal distribution of sky types in Burgos was determined, as presented in Figure 7. As can be seen, the sky types corresponding to clear sky conditions (11 to 15 CIE standard sky types) presented FOCs ranging from 71.72% in summer to 34.45% in winter. Sky type 12 was the most likely CIE standard sky type, with FOCs of 18.19% in winter, 21.21% in spring, 27.84% in summer, and 17.61% in autumn. Those figures imply VSC values higher than 45%, regardless of the scattering angle, with acceptable daylighting conditions throughout the year for dense urban design. Sky types corresponding to cloudy sky conditions (CIE standard 1 to 5) are more probable in winter and autumn.