SOLAR RADIATION AND ITS MEASUREMENT - Environmental UV Radiation: Impact on Ecosystems and Human Health and Predictive Models - page 34

Figure 11. Schematic drawing of a Solar Light UV-Biometer ® 501 (http://www.solar.com).
Spectral mismatch . The agreement of the spectral response of the detector and
the corresponding action spectrum is of major importance in broadband radiometry. An
example illustrates how large errors build up if broad band instruments are employed
inadequately. Even if the agreement between the CIE erythemal action spectrum and the
actual spectral response of a R-B meter (Figs. 12a and 12b) is quite satisfactory in the
UV-B range there is a considerable spectral mismatch at wavelengths below 280 nm.
Therefore, the R-B meter reading and the calculated erythema effective irradiance are
virtually the same if terrestrial solar radiation is registered (Fig.12a). Measuring the
emission of a sun ray lamp with strong lines in the UV-C, however causes detector
reading and true erythema effective irradiance to differ by a factor of almost 4. The
instrument is certainly not designed for this application. The example however, should
draw the attention on the spectral mismatch as a source of error.
Due to their wavelength integrating characteristics broadband meters are not
very sensitive to small changes in the spectral composition as those caused by small
changes in the stratospheric ozone concentration. Broadband radiometers are however,
much easier to handle and less expensive than spectroradiometer systems. Therefore,
they are very useful in the long-term monitoring of a variable radiation environment.
Besides photoelectric radiometers UV-dosimeters based on biological or
chemical reactions are sometimes employed mainly for personal dosimetry. These
devices are reviewed in detail in the article by Horneck in this topic 21 .