What is the UV index?
The UV index is a measure for the intensity of the UV radiation from the Sun at the surface of the Earth.
The UV index was created to inform the public about the expected level of UV radiation at the surface of the Earth.
Originally, the UV index was formulated independently in several countries and used in programs for public information about UV radiation. Its definition has later been standardized and published as a joint recommendation by the World Health Organisation (WHO), the World Meteorological Organisation (WMO), the United Nations Environmental Program (UNEP) and the International Commission on Non-Ionizing Radiation Protection (ICNIRP), in order to raise public awareness about the potential detrimental effects on health from solar UV exposure and to alert people of the need to adopt protective measures.
The UV index is defined as the effective irradiance on a horizontal surface obtained by integrating the spectral irradiance weighted by the Commission Internationale de l’Eclairage (CIE) reference action spectrum for UV-induced erythema on the human skin up to and including 400 nm and normalized to 1.0 below 298 nm (see also Fig. 2).
The UV Index is a number describing the effect of the intensity of the solar radiation on the unprotected skin. The different classes of the UV index and their effect on sunburn are summarised in the table below.