Index). This parameter is an indicator of the erythemally weighted UV radiation at surface. It is defined as the integration of solar irradiance (280â400 nm) ...
SUN EXPOSURE GIUSEPPE R CASALE1*, ANNA MARIA SIANI1, ALFREDO COLOSIMO2 *Corresponding author 1. Department of Physics – Sapienza Università di Roma, Piazzale Aldo Moro 2, 00185 Rome, Italy. 2. Department SAIMLAL – Sapienza Università di Roma, Piazzale Aldo Moro 2, 00185, Rome, Italy.
Giuseppe R. Casale
A UV Index sundial on compact disk KEYWORDS: solar ultraviolet (UV) radiation; UltraViolet Index (UVI); phototype; compact disc (CD); radiative transfer model; sunburn time; erythema
Abstract
This paper provides information on the capability of a compact disk (CD) of estimating the UVI (Ultra Violet Index). This parameter is an indicator of the erythemally weighted UV radiation at surface. It is defined as the integration of solar irradiance (280–400 nm) measured on a horizontal plane, weighted by the erythemal (skin reddening) action spectrum, and properly scaled to become a dimensionless number. The UVI is widely used as an indicator of UV levels at the earth’s surface providing public awareness of the effects of prolonged exposure to the sun’s rays. Our CD based device is designed for personal use and may become a valuable tool for a better communication of the UVI to the public with the hope to draw people’s attention to use it and to adopt adequate sun protection behaviours.
INTRODUCTION The ultraviolet (UV) band of the solar spectrum is characterised by wavelengths in the range 200–400 nm but only a small fraction of the total solar flux density at the top of the atmosphere reaches the earth’s surface (1). The amount of surface levels of solar UV radiation depends on astronomic, geometric and atmospheric factors which determine daily variability, day-to-day changes and seasonal/annual variations. After the discovery of the so called Antarctic “ozone hole” in 1985, solar UV radiation has become an important environmental, ecological and atmospheric parameter to be studied and monitored (2). The terrestrial solar UVA (320-400 nm) and UVB (280-320 nm) bands have a potential biological risk for humans. Solid experimental and epidemiological studies have shown that solar UV exposure lies behind some types of skin and eye disorders (1): the erythemal reaction is the well-known acute effect on human skin (visible as reddening mainly in fair-skinned people) due to prolonged solar UV exposure. However, absorption of small amounts of UV radiation has also beneficial effects, as the initiation of vitamin D production, which is of great importance for bones’ health (3). Consequently, it appears of great importance to disseminate information to the public about the UV levels and for this purpose a dimensionless index, the UltraViolet Index (UVI), was internationally adopted (1) by the World Meteorological Organization and the World Health Organization in 1994. The UVI can be either retrieved by measures or determined by means of models. In our previous study (4) we developed a novel device to estimate the UV Index based on the use of a compact disk (CD) demonstrating its feasibility as UVI sundial. The aim of this paper is both to extend the previous work by providing the sunburn times for each phototype, as a function of UVI readings provided by the CD, and to show how it can be easily used with the hope to prompt sun protection behaviours in the users.
THE COMPACT DISC FOR ESTIMATING THE UV INDEX The effectiveness of UV radiation in causing a specific reaction within a biological system can be described by weighting functions (or action spectra) generally normalized to unity at the wavelength of maximal sensitivity. The UVI is calculated as the integral of the spectral solar UV irradiance at a horizontal surface weighted with the CIE erythemal action spectrum (5) and divided by 25 mW m–2. UVI values can range between 0 (during the night) up to 20 (6). The UVI can be categorized in: low (UVI
