Erythemal effective UV radiation
The Erythemal effective UV radiation (in German: sonnenbrandwirksame UV-Strahlung) plotted on the Y axis is the biologically weighted radiation being responsible for the sunburn (erythema). It results from an integration of the physical UV irradiance (in the unit W/m²) at ground level weighted by the wavelength-dependent biological sensitivity of the skin to get sunburnt (Erythemal action spectrum). The dimension of erythemal effective UV radiation is also power per area. As the occurring values are considerably smaller than 1 W/m² generally the unit mW/m² is used (1 mW/m² = 0.001 W/m²). On the X axis the time ME(S)Z means Central European (Summer) Time CE(S)T.
The UV Index is an internationally standardized measure of this sunburning effect of UV radiation. It is derived as an integer value without unity from the measured (or modeled) erythemal effective UV irradiance on a horizontal surface. The current UV index (in the figures "today" and "yesterday" in the daytime top right in the blue box) is calculated as a moving average over the last 10 minutes and varies throughout the day. The daily high of the UV index (UVImax) is the highest UVI of a day averaged over a period of 30 minutes. If the current UV index is known, suitable protective measures may be taken. For detailed information on the UV index and its application, see e.g. at the World Health Organization WHO.
The figure shows, on the one hand, the measured values of the erythemal effective UV radiation, which is recorded every minute and displayed as colored bars. In the figures "today", "yesterday" and "last week", in addition to the measured values the theoretical daily course for cloudless ("clear sky") conditions (gray curve course) is given. In the representations "Last month" and "Last year", the gray-shaded curve corresponds to the course of the calculated daily maximum values (noon values) of the erythemal effective UV radiation for cloudless conditions.
The sensor used here is a broadband radiometer of the type UV-Mess-Sonde UV-Cosine_UVI of the company sglux, Berlin, DE.