###### Abstract
However, the increasing number of such projects does not correspond to the importance that circadian light should have according to relevant indoor studies. A lack of knowledge has revealed how the characteristics of outdoor daylight are considered to perform indoor lighting designs. Beyond visual stimuli, the CIE S 026/E: 2018 standard [10] includes information concerning the effects of light on intrinsically photoreceptive retinal ganglion cells (ipRGCs) that are related to the SPD, temporal distribution or photoperiod: dynamic light, which is the right light at the right time [11; 12]. Even the International WELL Building Standard (Visual lighting design and Circadian lighting design) recommends lighting guidelines to provide appropriate photopic and scotopic light levels, minimize disruption to the body's circadian system, and support good sleep quality [13]. Currently, lighting projects consider that the circadian rhythm in humans is described as an approximately 24 h cycle controlled by the lighting environment and one of the keys to regulating sleep, mood, heart rate and body temperature [14]. Nowadays, people stay indoors with artificial lighting and with relatively limited sunlight most of their time awake, or under the influence of secondary sources such as screens; these environmental contributions should be globally evaluated in circadian terms [15]. The CIE divides the visual from nonvisual effects of light and is developing integrative standards from this perspective [10]. To fulfil this objective, special attention has to be paid to the SPD. Both the excitation of traditional photoreceptors and ipRGCs are highly wavelength-dependent and form two interdependent pathways for light in the brain [16]. To evaluate and quantify the visual and nonvisual influences of light in humans belonging anatomically to these two ocular pathways, the CIE adopted the proposal of [PERSON] et al. defining that the influences are physically characterized by five equivalent \(\alpha\)-opic illuminance approaches. This standard employs light measurement methods that quantify the effective irradiance for each of the photoreceptive inputs to the visual system independently. The CIE S 026/E:2018 [10] adopted melanopic equivalent daylight (D\({}_{65}\)) illuminance, which the Equivalent Daylight Illuminance (EDI) defined as a light source-type D\({}_{65}\) that employs photopic illuminance E\({}_{photopic,D65}\) to provide the same melanopic irradiance as a light source with the SPD and photopic illuminance E\({}_{photopic,SPD}\). An important issue found for accurate visual and nonvisual daylight implications is the limited information available for this analysis because at least six factors triggering nonvisual light effects have been summarized, including the SPD, the irradiance level, the directionality, the timing, the duration, and the history, which are grouped into luminous and temporal categories [11]. Nevertheless, there have been efforts to develop a clear method to evaluate the effects of lighting on circadian rhythm regulation from different perspectives [17; 18]. This research hypothesizes that daylighting SPDs modify the photopic and melanopic levels inside buildings depending on the orientation, seasonality and characteristics of the skydome [17; 18]. The aim of this study is to analyse these real seasonal changes in natural sunlight to evaluate how changes in the SPD affect photometric quantities and calculate the variations in circadian magnitudes based on the CIE standard. Knowledge of the outdoor daylight is essential to achieve a good natural lighting design in indoor areas from a wellbeing perspective. Differences in daylight with geographical location of a building, facade orientations or seasonality should be analyzed and considered to evaluate the nonvisual potential of daylight for indoor lighting purposes. This analysis leads us to evaluate the main parameters that should be considered by indoor designers to simulate daylight conditions with artificial lighting promoting people's wellbeing.