Ultraviolet A dosimetry in photopatch test centres in Europe

The aim of the study was to investigate the state of ultraviolet (UV) A dosimetry in photopatch testing centres in Europe.

It has been acknowledged that a widespread disparity exists in the way photopatch testing is carried out in different countries throughout Europe. This prompted the formation of a European taskforce that developed a consensus methodology. One issue that was not addressed directly was that of UVA dosimetry, which clearly impacts on the consistency of the clinical results.

Ten UV meters from photopatch test centres throughout Europe were set up at a reproducible position from a photopatch test light source containing UVA fluorescent lamps and the irradiances were noted from each meter. One meter served as a reference meter with calibration carried out in an optical laboratory traceable to the National Physical Laboratory.

The mean of all the measurements was 5.74 mW/cm(2) with a SD of 0.36 mW/cm(2). Expanded uncertainty at 95% confidence level was 12%.

It is desirable that meter calibration should have an accuracy of the order of +/-10%. The variation in recorded values among the 10 meters investigated was within acceptable limits. The meter must be calibrated using a similar light source to that used in the phototest equipment, in this case a UVA fluorescence lamp.