The global solar UV index (UVI) was developed as an easy-to-understand measure of biologically effective UV radiation with a view to promote public awareness of the risks of UV radiation exposure and sun protection, using the CIE erythemal action spectrum as basis.
Read our Eyrthema amd skin exposure to UV application guide for more details.
In the initial work done on UVI in Canada, a typical midday summer erythemal irradiance of 250 mW.m-2 was found, leading to the definition of one UV index equal to an erythemally weighted irradiance of 25 mW.m-2. This gives a typical range from UVI 0 at night to UVI in excess of 11 in sunnier climes.
UVI can be evaluated directly through a measurement of global solar irradiance in a location with an un-obscured hemispherical view. The spectral range can be reduced to 290-400nm given that the shorter wavelengths aren't transmitted to the earth's surface thanks to the ozone layer.
- "Global Solar UV Index - A Practical Guide." A joint recommendation of: World Health Organization, World Meteorological Organization, United Nations Environment Programme and International Commission on Non-Ionizing Radiation Protection