# Erythermal Solar Irradiance, UVER, and UV Index from Ground-Based Data in Central Spain
## 3 Results
### Cumulative Doses for Four Different Skin Types  
To understand the different cumulative dose evaluations for various skin types, it is worth looking at some definitions, variables, and concepts. It is known that the standard erythema action spectrum  
Figure 4: Ultraviolet index (UVI) index differences between values at solar noon and the maximum daily UVI (integer UVI units) in Valladolid, Spain, for the period 2013–2019. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & & \multicolumn{3}{c}{UV Index (\%)} \\ \hline UVI & 0–2 & 3–5 & 6–7 & 8–10 & 11- \\ \hline  & Low & Moderate & High & Very high & Extreme \\ \hline UVI (\%) & 32.4 & 21.1 & 17.2 & 28.9 & 0.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Days (in %) during the years studied where the shown maximum UVI values are reached. shows an internationally accepted representation of the erythema caused by the UV wavelength spectrum parts. It is defined as a spectral UV capacity to produce erythema in human skin. In addition, the action spectrum form is used for public health information and forms part of the standard erythema dose unit (SED) and the minimum erythema dose (MED). The action spectrum of a biological effect describes the wavelength-dependent response for the irradiance. In UV studies, we have observed that different variables, such as UVI, SED, and MED, have been defined, and it is known that UVI indicates the instantaneous sunburning potential of solar irradiance; total erythema radiation received can be expressed in terms of the standard erythema dose unit (SED), where one SED is defined as 100 Jm\({}^{-2}\). The minimum erythema dose (MED) is the minimum dose of erytomal irradiance that produces faint but perceptible reddening of the skin 24 h after receiving irradiance. In addition, the MED is not a standardized term but a personal measure of susceptibility to sunburn. Derived units are thus based on the erythema action spectrum. As a conclusion, the erytomal action spectrum, (S\({}_{\text{er}}\)(\(\lambda\))), should be defined as the spectral dependence of UV capacity to produce erythema in human skin. Erythermal effective irradiance, UVER, is the product function of spectral irradiance and its erythema action spectrum [9] integrated over the wavelength. In this section, the relationship between maximum daily UVI and the cumulative daily dose in SEDs is analyzed using measured daily UVER data. In addition, to do this the main characteristics of four skin types, as well as the dose required to produce one MED shown in Table 2, are used. As a result, the yearly cumulative dose for each skin phototype is shown in Figure 5. The Standard Erythermal Dose curves, SED and MED, were obtained by dividing the daily UVER values by the corresponding MED and SED values over an average year at the measurement site. The results indicate the erytomal irradiance received throughout the year in a horizontal position and for continuous and uninterrupted exposure to the sun. Figure 5 shows that the cumulative doses during an average year reach 8921 SEDs in Valladolid. Table 2 shows the main characteristics of four skin types used to carry out the evaluations. The most common skin type in Valladolid, Spain, is phototype II and Figure 5 shows how it could receive an annual cumulative dose of 3559 MED (blue curve). Figure 5: Yearly cumulative dose (minimum erythema dose—MED) for different skin types defined by ISO 17166 CIE S 007/E and Standard Erythermal Dose, in Valladolid, Spain, for the period 2013–2019. Figure 5 depicts a clear change in the slope in the cumulative curves in summer (June, July, and August). When the cumulative doses are estimated for each season, we observe that 47.06% of the annual cumulative dose is received in summer, 28.38% in spring, 18.13% in autumn, and 6.42% in winter.