Environmental Engineering Reference
In-Depth Information
sensitivity to UV-C and UV-B, whereas for longer wavelengths (300-365 nm) the cells
of the normal type seem to become more sensitive than the XP cells, by up to one order
of magnitude. This is certainly not the case, as demonstrated by the absolute action
spectra. Much confusion could be avoided, if always absolute values of the original
action spectra were available. Therefore, when using relative action spectra for
comparing different biological UV responses or different strains for the same response,
the absolute response at least to the reference wavelength has to be known for each
endpoint or strain 7 .
10 -17
10 0
10 -18
10 -1
10 -19
10 -2
10 -20
10 -3
10 -21
10 -4
10 -22
10 -5
10 -23
Xeroderma pigmentosum
normal
Xeroderma pigmentosum
normal
10 -24
10 -6
240
260
280
300
320
340
360
380
240
260
280
300
320
340
360
380
A
B
Wavelength, nm
Wavelength, nm
Figure 5. Absolute action spectrum of normal and XP cells (A) and relative action spectrum of the
same cells scaled to one at 254 nm (B) (data from ref. 23).
For assessing risks from environmental radiation, the most widely used action
spectra are that for DNA damage, for cancer induction, and for UV induced minimal
erythema in human skin, which has been defined by the CIE (Commission International
d'Éclairage) as erythema reference action spectrum (CIE MED spectrum) (Figure 4).
Weighting broadband radiometry
Different types of broadband radiometers have been developed that measure the
irradiance of a defined UV band, e.g., UV-B or UV-A (see Häder, this issue). Several of
them have spectral sensitivity similar to a specific biological response function, e.g., the
CIE MED spectrum. However, because the spectral sensitivity curve of most
biologically weighting broadband radiometers does not perfectly match with the most
relevant action spectra, e.g. the CIE MED curve, their readings must be corrected with
regard to the spectral irradiance of the UV emitting source and the action spectrum
according to
(4)
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