Environmental Engineering Reference
In-Depth Information
damage may be repaired by enzymatic and other repair mechanisms and cellular
apoptosis. 7
Luminous exposure (photometric) and radiant exposure H are both quantities
used to describe a total exposure dose from a flashlamp or from a more lengthy
exposure. While both E and H may be defined over the entire optical spectrum, the
luminous exposure is only defined over the visible spectrum and is therefore not of
value in UV photobiology. Where radiant energy is more penetrating, as in the visible
and IR-A spectral bands, it is sometimes useful to apply the radiometric concepts of
fluence and fluence rate as shown in Figure 3. 7 For all photobiology, it is necessary to
employ an action spectrum for photochemical effects.
The relative action spectra for both UV hazards to the eye (acute cataract and
photokeratitis) are shown in Figure 5. 2,7-9 These effects will be discussed in greater
detail later. The UV safety function S(Ȝ) is also an action spectrum, which is an
envelope curve for protection of both eye and skin, is shown in Figure 6. 2,7
Figure 5. Action spectra for injury to the lens and cornea by near UV radiation. Lower solid curve is
the data of Pitts, Cullen and Hacker (1977), for photokeratitis; upper dashed line is the data for
permanent lenticular opacities; intermediate dot-dash line with open squares is the threshold for
temporary lenticular opacities. The open circles with dashed lines represent threshold for corneal
injury by Zuclich and Kurtin (1977).
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