A study of the directional response of ultraviolet radiometers: II. Implications for ultraviolet phototherapy derived from computer simulations

A theoretical model has been used to simulate irradiances for ultraviolet ( UV) phototherapy cabinets and other sources. The accuracy of the simulation results has been checked by comparison with experimental measurements. The simulations have been used to study the influence of different factors on UV phototherapy exposure and to develop recommendations for the operation a nd calibration of phototherapy cabinets. Many radiometers used in the evalu ation of skin doses have input optics with directional responses that are n ot proportional to the cosine of the angle of incidence for the UV radiatio n. Data on radiometer directional responses have been incorporated into the simulations, which show that the poor directional responses for some radio meters currently in use will give errors of 20-50% in the assessment of irr adiance. The influence of lamp source geometries employed for radiometer ca libration has been investigated. UV phototherapy dosimetry commonly uses a spectroradiometer and a radiometer in the transfer of irradiance calibratio ns from a small standard UV lamp to a large-area source with a different UV spectrum. Recommendations are given on the range of acceptability for radi ometer directional responses and a method is described for determining whet her these are fulfilled. Recommendations are made on the techniques that sh ould be used for calibration.