UV Index

The UVI is a measure of the intensity of UV radiation on the Earth’s surface that is relevant to effects on the human skin. UV radiation levels and therefore the values of the index vary throughout the day. In reporting the UVI, most emphasis is placed on the maximum UV radiation level on a given day. This occurs during the four-hour period around solar noon. Depending on geographical location and whether daylight saving time is applied, solar noon takes place between local noon and 2 p.m. The media usually present a forecast of the maximum UV radiation level for the following day. UVI values are grouped into exposure categories.



Source: Global Solar UV Index - a Practical Guide