Midsummer solar UV-radiation in Finland compared with the UV-radiation from phototherapeutic devices measured by...

Midsummer solar UV-radiation in southern Finland was measured by a spectroradiometer, polysulphone film dosimeters, and a solid-state UV-meter. Solar UV-irradiance was compared with radiation from different phototherapy devices (UVB, SUP, and PUVA therapy equipment). Measured by the spectroradiometer, the solar UVB irradiance at noon was 55 microW/cm2; it varied from 60 to 79 microW/cm2 according to the doses received by the film dosimeters on clear, sunny days in June. A solid-state detector gave a markedly overestimated UVB irradiance of 235 microW/cm2. Solar UVB radiation would lead to 1.5 MEDs in 2 hours around midday, 2.9 MEDs in 4 h and 8 MEDs in 12 h in midsummer at latitudes in southern Finland. Solar UVB radiation corresponds to that emitted from PUVA treatment devices, but the UVA (315-400 nm) radiation of the latter is about 3-fold that of solar radiation. The UVA radiation from SUP and PUVA treatment devices resembled each other but the former emitted more radiation at the lower wavelengths of 315-340 nm. The UVB irradiance of the UVB therapeutic device was 25-55 times the irradiance of the sun.