Accurate calibration of ultraviolet (UV) radiometers is very important in phototherapy and photobiology research to ensure that UV doses are comparable between centres. Several medical physics departments in the UK provide a service to calibrate UV meters traceable to national standards. However, there is concern that there may be disagreement between departments and in particular that there may be specific difficulty in calibration for the newer narrow band UVB phototherapy lamps (Phillips TL01).
The aim of this work was to ascertain the level of agreement in UV meter calibration at expert centres in the UK. Also to briefly survey methodology at these centres, consider sources of errors and to make recommendations on calibration methods.
A UV meter with two UV probes (for UVA and TL01 lamps) was sent in turn to 7 centres and each provided relative calibration factors. A questionnaire on methods was also distributed and measured spectral outputs from each centre were examined. The calibration factors for the meters varied by around ±20% for the UVA probe and ±40% for the TL01 probe (2 standard deviations). 6 centres performed calibration using a spectroradiometer and one centre used a reference meter method. The spectra of lamps used for calibration were similar. For the spectroradiometric methods there were some differences in methodology and instrumentation that may account for the differences in calibration factors.
UV meter calibration in the UK shows unacceptable variability, particularly for TL01 lamps. This may hinder advances in photobiology research. An accuracy of around of ±10% would be clinically acceptable and should be technically achievable. Some recommendations on calibration instrumentation and methodology are made and it is suggested that this intercomparison exercise should be repeated.
Lloyd JJ. Uncertainty in calibration of UV radiometers. British Society for Investigative Dematology Annual Meeting 2003, University of Southampton, UK. Abstract published in British Journal of Dermatology. 2003; 148: 865-866.
Dr. Jim Lloyd, RVI Unit, Newcastle upon Tyne. Tel: +44 (0)191-233-6161.
Regional Medical Physics Department, Newcastle General Hospital, Newcastle upon Tyne, NE4 6BE, UK.
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