Units for measuring ultra-violet radiation
The ultra-violet radiation flux can be expressed in units of watt/m2, but in order to illustrate the significance of the measurement, MED (Minimal Erythemal Dose) units are used. These units are defined as the amount of radiation that causes a minimal reddening of white, un-tanned skin. However, a special UVB index was developed, which is expressed in non-dimensional units (equal to the amount of the radiation flux in milliwatt divided by 25) The scale of the index ranges from 1 to 13 , with 1 also including all lower values, and a value of 11 or higher categorized as extreme. These units appear in the legend.