Measurement of daylight UVA in Glasgow

Measurements of daylight UVA have been carried out in Glasgow using a UVA-band detector and a spectroradiometer, both with the aperture window horizontal. Daily energy densities, defined as the total UVA energy each day per unit area, were obtained for the period November 1980 to May 1982. Levels rose from a mean December daily energy density of 4 J cm-2 to an average of 69 J cm-2 in June, with considerable fluctuations from day to day and with up to seven-fold changes observed on consecutive days. The UVA level sometimes varied rapidly during the day, with differences of up to a factor of six in successive 10 min periods. The daily temporal distribution of UVA for summer and winter, and the measured daylight spectra are presented. The spectroradiometer contained a double-grating monochromator used at a band-width of 1 nm. Measurements made by the spectroradiometer were compared with earlier published findings o solar UVA doses received by 56 patients who were photosensitized by 8-MOP in the course of PUVA therapy. It is shown that the median dose represented only 12 min daylight exposure and this indicates that the majority of patients to take care to avoid unnecessary exposure. However, the maximum dose was equivalent to some 84 min exposure to daylight UV and so there is clearly scope for a considerable reduction in exposure in some cases.