According to the Shadow Rule (SR), an individual can control the time of exposure to the Sun observing the body's shadow length on a horizontalsurface. Although a simple rule, the SR depends primarily on the ozone column (O3) amount, which can complicate the application of this rule in scenarios of lower O3 amounts like those in the low latitudes of Southern Hemisphere. The SR by itself can be confusing and impractical for application, as the shadow length can be of uneasy grasp and high uncertainty use unless one is equipped with calculator and ruler. Using the daily distribution of erythemal dose rates in Belo Horizonte (BH, 19.92ºS, 43.94ºW, 858 masl, 331 km², Brazil) for a period of 22 months, this work shows that a warning on time for solar exposure can be a safer, more efficient and more practical procedure in terms of creating a culture of casual exposure to the Sun than the use of the SR. For tropical and equatorial Brazilian sites, the diurnal interval for the avoidance of dangerous solar incidence of ultraviolet radiation is that between 2.5 hours after sunrise and 2.5 hours before sunset.
solar ultraviolet radiation; shadow rule; UV-Index
