Possible Errors Involved in the Dosimetry of Solar UV-B Radiation

Abstract

Despite the increasing use of artificial sources of optical radiation in industry, medicine, science, and leisure pursuits, the sun still remains the most common source of UV radiation exposure to man. To obtain a quantitative understanding of the relationship between sunlight exposure and photobiological effects caused by exposure demands accurate and reliable dosimetry of solar UV-B radiation.

The most fundamental dosimetric technique is spectroradiometry; that is, determining the irradiance at the point of interest in a series of narrow, contiguous wavelength bands which cover the spectral range of interest. The optical components required to achieve these data are discussed, together with the parameters which affect the accuracy of such spectral measurements. In many cases spectral measurements are not required as ends in themselves, but for application to the calculation of biologically-weighted radiometric quantities. These quantities can be derived from the spectral data by a process of weighted integration over the range of wavelengths present in the spectrum.

An alternative and more common method of measuring solar UV-B radiation is to use a detector whose sensitivity varies with wavelength according to some prescribed weighting function. Probably the most widely-used device has been the Robertson-Berger meter which incorporates an optical filter, a phosphor and a vacuum phototube or photovoltaic cell. This device measures those wavelengths in the global spectrum less than 330 nm with a spectral response which rises sharply with decreasing wavelength, and has been used to monitor natural UV radiation continuously at several sites throughout the world. A different, yet complementary, approach is the use of various photosensitive films as UV dosimeters. The principle is to relate the degree of deterioration of the films, usually in terms of changes in their optical properties, to the incident UV dose. The principal advantages of the film dosimeter are that it provides a simple means of integrating UV exposure continuously and that it allows numerous sites, inaccessible to bulky and expensive instrumentation to be compared simultaneously. The most widely used photosensitive film is the polymer polysulphone. Polymer film UV-B dosimetry has allowed estimates to be made of erythemally-effective solar UV-B doses received by groups of people in different occupations and pursuing different leisure activities.