New National Research Center data on exposure to ultraviolet radiation
Sun radiation in the ultraviolet (UV) band, and in particular in bands B (280-320 nm) and A (320-400 nm) is recognized as being one of the main, potential health hazards for the body and, more specifically, for the eyes.
As it is now well known, some conditions have been identified in which UV radiation can exceed safety levels at our latitudes: the central hours of the day during summer and spring (when the sun's rays reach the earth more quickly because it is higher in the sky); high altitude (for the same reasons); clear skies.
It is also known that it is not only these conditions that make exposure hazardous: even with certain types of cloud cover, the number of UV rays reaching the earth is higher than our senses can perceive.
To date, however, the prevailing research approach has been strictly meteorological and, as a result, the reference has been the irradiation of horizontal reference surfaces.
Wishing to apply the available knowledge on safeguarding health, and in this specific case, sight, the Biometeorological Institute of the National Research Center in collaboration with the Vision Defense Commission and as part of the 'Sun Project', has begun a survey aimed at characterizing the quantity of biologically effective UV radiation on vertical surfaces which, at this early stage at least, can be used as a reference for the face of a person in the vertical position. This entails that not only all the aspects of sun-surface geometry have to be reconsidered, but the contribution made by the surrounding environment can no longer be ignored.
The results not only confirm and quantify certain data about the effect of the sun's angle on horizontal surfaces, and the atmospheric transparency and altitude conditions, but it has also been possible to quantify the influence of radiation reflected from the ground and the surrounding environment. In the case of snow-covered ground, approximately 80% of UV radiation incidence can be reflected and makes a significant contribution to radiation on non-horizontal surfaces. Even greater values are obtained in the blue band.
Especially for this reason, the measurements taken on vertical surfaces have revealed that in March (on snow) values are considerably higher than in the summer (on sand or grass). Therefore, in specific conditions, even in seasons marked by low or moderate levels of sun radiation, ultraviolet radiation can represent a serious danger to health and eyes.
This is even more important when considering that in general the systems used to forecast and measure UV radiation refer to horizontal surfaces (and therefore ignore any reflection phenomena). Taken to the extreme, on specific types of ground, the reflection component alone (for example, with the sun behind or in the shade of an umbrella) can be sufficient to cause high values of UV radiation which can reach the eyes.
A study of the effectiveness of a beach umbrella for reducing radiation incidence showed that it blocks around 90% of radiation incidence on a horizontal surface underneath, however, in the case of vertical surfaces; however this effectiveness can fall to 40% (whether the surface underneath is snow or sand) and therefore even in the shade, and especially where particular solar angles and ground characteristics are concerned, UV radiation values can reach levels that endanger health.
Moreover, most of the damage linked to ultraviolet radiation is accumulated and therefore prolonged exposure to UV radiation, even of a low or moderate intensity, requires adequate precautions, including the use of sunglasses.
