BASIC CONCEPTS OF RADIATION - Environmental UV Radiation: Impact on Ecosystems and Human Health and Predictive Models - page 14

the choice of a narrow bandwidth leads to low “throughput” of spectral radiant energy
and therefore long exposure sessions. Also, “stray light” outside the spectral band-pass -
particularly from gratings - lead to errors from out-of-band radiation. 11,12
Distorted action spectra can be produced when one uses high-intensity
monochromators using arc-lamp sources. Overly broad bandwidth or stray light will
lead to a distorted, erroneous action spectrum. Plotting threshold data at the
monochromator wavelength setting is reasonable only if the action spectrum is not
changing rapidly. Changing action spectrum requires narrow spectral bandwidths for
resolution. 2,7
Figure 7. Example of a distorted action spectrum. The “true” action spectrum is the 1 nm bandwidth
inner curve. A 5-nm bandwidth produces a wider, erroneous curve.
The accuracy, and reliability of any hazard evaluation or risk assessment of an
optical radiation hazard depends strongly upon the accuracy and precision of the
relevant action spectra employed. The occupational and environmental health
committees of experts which derive human exposure limits used in safety standards and
risk assessments rely heavily upon the accuracy of the action spectra obtained by
photobiological research. It is therefore important to recognize the factors that influence
the quality of the original photobiological research, the possible sources of error and the
levels of uncertainty in applying laboratory action spectra to human health risk
assessment. One need only study the variation in the reported action spectra published
by different laboratories for the same biological effect to recognize that the derivation of
sound action spectra is surely fraught with some problems. Both biological and physical
factors influence the variation in published action spectra. Biological factors which may
affect the actual biological effect of exposure to optical radiation include: variation in
response among species, variation in response due to individual adaptation, influence of
foods and pharmaceuticals, the biological endpoint applied in each study, and the means