Ozone, UV and Aerosol studies

You are here: Ozone, UV and Aerosol studies » UV » What is the UV index?

UV index definition

The yellow line shows the intensity of the solar light at the top of the atmosphere between 280 and 400 nm. The blue line represents the intensity on a horizontal surface at the ground, typically on a clear summer day noon at mid latitude. The line in cyan is the CIE Reference Action Spectrum for Ultraviolet Induced Erythema of Different Human Skin Types. When the spectrum at the ground is multiplied with this action spectrum the result (red line) is the effective irradiation at the ground. These values are integrated between 280 and 400 nm and multiplied by 40 to yield the UV-index (indicated by the red-shaded area).

The different classes of UV index and their effect on sunburn are summarised in the table below.

UV-Index UV-Intensity Skin burns
0-2 low almost not
2-4 moderate slowly
4-6 moderately high easily
6-8 high fast
8-10 very high very fast
>10 extreme almost immediately