Ultraviolet radiation monitoring. Solar radiation monitoring system at the summit of Mount Snowdon, Wales. This instrument measures and records ultraviolet A (UVA) radiation, visible light radiation and erythemally weighted UV radiation, which is the wavelengths of UVB and UVA radiation that cause the most damage to skin. This is part of a network of instruments that measure terrestrial solar radiation at different latitudes. The network provides information on the range of variation of UV radiation at different latitudes, at different times of the year, and the effects of cloud cover.