## 3 Results and Discussion
### Circadian Characteristics
[29], CL\({}_{\text{A}}\) provides information on the SPD at the corneal level converted into circadian light [30; 31]; and the CS, based on the CL\({}_{\text{A}}\), is equal to the percentage of melatonin suppression [32], ranging from threshold (CS = 0.1) to saturation (CS = 0.7) [33]. The CS seems to be necessary to promote circadian entrainment. As our mean CS obtained is 0.695 \(\pm\) 0.004 with a variation of 1%, it could be considered sufficient for the described saturation. Therefore, CS could be used directly to quantify the circadian impact of lighting. The values calculated in our study show that there would be a high percentage of melatonin suppression independent of the seasonality, orientation and elevation. Studies show that a CS equal to or greater than 0.3 (equivalent to 30% melatonin suppression) in the first part of the day can improve the circadian cycle and the quality of sleep, reduce drowsiness and increase vitality and alertness [31; 33; 34; 35], which coincides with our data collected from 10:00 to 11:00 AM. A value of CS = 0.35 was proposed as a sufficient and adequate value to promote the daily cycle [36]. According to [PERSON], the daylight spectrum has been shown to be relatively efficient in providing circadian stimulation; and based on the CIE D\({}_{65}\) spectrum, a corneal illuminance of 233 lux corresponds to this 0.35 CS. Extrapolating our outdoor analysis to indoor situations, circadian efficiency should be treated with caution because artificial lighting seems to be less effective since for the same value of CS = 0.35, a corneal illuminance much higher than that necessary with natural light would be needed [37]. All the outdoor SPDs collected for this paper are, regarding the CCT, above 4800 K, meaning that for indoor lighting purposes, it would be equivalent to cold light; and, assuming the same light intensity, higher CCT values indicate a greater perception of luminosity. This fact could improve visual performance and the relative effectiveness of light sources with higher melanopic intensity. This situation will be favourable for improving indoor performance in the morning hours; however, in the afternoon and at night, it will be more convenient to use warm lighting with low melanopic intensity [9; 15]. In an investigation of a method to evaluate the nonvisual potential of daylight in two European cities, CCTs between 4631 K and 11,871 K were recorded in Naples and CCTs between 3585 K and 9812 K were recorded in Bialystock [17]. These results are similar to those of this study since our CCT measurements vary between 4892 and 12,380 K. However, due to the low correlation between the CCT and circadian effects, it is considered that the CCT is not a good indicator to establish the levels of circadian response [20; 37]. Although [PERSON] et al. reported that LEDs with high CCTs above 5299 k could slightly stimulate the circadian system after one hour of exposure to outdoor lighting at 95 lux, when taking advantage of natural light in interior spaces, the reflectance of the walls must also be considered because they vary the CCT and the spectral composition of light that regulate the circadian system [38; 39; 40]. Additionally, our measurements show that for indoor purposes where daylight reaching outdoors is important, new parameters, such as the seasonality, facade orientation and altitude of the sun, are substantial and have sufficient contributions that should always be considered. Figure 7: CS 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).