By Marc Pissavini
Abstract
Objectives: In this study, we quantify both the UVB and UVA doses emitted bythe sun at ground level and the realistic effective UVB and UVA doses received(ERD) by an individual across latitudes from 0° to 60° North and for every monthof the year. These outputs provide a quantitative basis to derive protectionindices and to support informed discussion on photoprotection. Our aim is notto prescribe SPF guidance for consumers or dermatologists, but to offer a robustscientific framework that clarifies how real-life exposure, behavioural factors,effective UVB and UVA-weighted doses and solar geometry collectively shapethe necessary UV protection.
Methods: Daily UV doses were computed for the 21st day of each month tocapture seasonal extremes. These doses, expressed as Standard Erythemal Doses(UVB) and UVA- weighted doses, were calculated for each latitude based onDiffey’s spectral irradiance framework. Two corrective factors were applied: (i)effective outdoor exposure time and (ii) body orientation. These adjustmentsallowed conversion of ambient daily doses into effective UVB and UVA-receiveddoses (ERD). Finally, a third factor, representing realistic sunscreen applicationdensity (0.8 mg/cm2), was introduced to estimate the necessary level of UVprotection.
Results: Across all latitudes and seasons, UV-weighted doses requirements followpredictable patterns driven by solar geometry. At most temperate latitudes, dailySED values range from approximately 5 to 60, while extreme values of 65–70 SEDoccur in tropical regions (10–30° N). The greatest differences between latitudesarise from seasonality. UVA-PF requirements exhibit similar constraints.When converted into effective received dose and then expressed in SPF terms,values above 60 provide minimal additional UVB benefit under realisticconditions.
Conclusions: By converting ambient irradiance into effective received dose,this model provides a realistic framework for daily UV exposure. It complements
