ABSTRACT
Quantitative phototoxicology requires appropriate dosimetry. The important
concepts, terminology and units of optical dosimetry required in photobiology
are all too frequently not fully appreciated in experimental studies, leading
to needless misinterpretation and error. The objective of this chapter is to
familiarize scientists working in photodermatology with the basic concepts
related to light measurement and light source characterization that are necessary
for reproducible scientific tests. Hopefully this chapter will encourage the reader
to look differently at the optical source being used and how correctly to express
the exposure dose. Phototoxicological studies require knowledge of the optical
and radiometric parameters of ultraviolet optical sources and geometrical
exposure factors. This knowledge is required to accurately determine the
irradiances (dose rates). In performing any phototoxicity study, it is imperative
that the spectral characteristics of the optical source must be known. For a
specific photobiological action spectrum, different light sources delivering the
same optical power can produce completely different dermatological effects if
the sources have differing spectra (Figure 45.1). Indeed, a photodermatologist
will choose a specific ultraviolet (UV) source to match best a given biological
action spectrum (if known) in order to achieve the greatest efficiency in
delivering a photobiologically significant dose. Different applications require
different light sources and a variety of measurement techniques may be in order
when attempting to conduct different types of studies. Photochemical inter-
action mechanisms are normally most pronounced at short wavelengths (UV)
where photon energies are greatest, and also will be most readily observed for
lengthy exposure durations (Sliney and Wolbarsht, 1980; WHO, 1994).
