Protecting Workers from Ultraviolet Radiation - icnirp

Protecting Workers from Ultraviolet Radiation
If the source is larger than 80° and the field of view of the instrument is not limited, then the
exposure level is overestimated. For skin measurements, the angular dependence of the
sensitivity of the detector within the field of view should be following a cosine law (see next
paragraph). Due to the difference of the field of view for measurements for skin or eye
exposure, for sources which subtend an angle larger than 80° at the distance of evaluation, the
exposure level which is compared to the exposure limit will be different (less for the eye than for
the skin). Therefore, although the UVR exposure limit is the same, since the exposure level for a
given source and exposure distance, might be different, the exposure of the eye might be below
the exposure limit while the exposure of the skin might be above the exposure limit.
8.5.3 Cosine dependence
The dependence of the sensitivity of the detector on the angle of incidence of the radiation
should follow a cosine dependence. Thus the detector mimics the directional sensitivity of the
human skin, which is assumed to be a plane surface. However, this is relevant only for sources
which are extended, i.e. non-point sources. The larger the source is, the more important it is that
the detector features a good cosine response even up to larger angles off the normal.
8.5.4 Spectral responsivity
The spectral responsivity of the detector should ideally be identical to the applicable action
spectrum. This is the biggest practical problem encountered with the use of UVR meters.
Radiation outside of the wavelength range over which the action spectrum is defined should be
rejected, i.e. not contribute to the measured value. Some UV-detectors and spectrometers are
also erroneously sensitive in the visible region. As the visible radiation level of the source being
measured is often much higher than the UV-level, this may severely compromise the accuracy of
the measurement. Without a specific calibration of the broadband meter for the source that is to
be measured, it is not recommended to use broadband meters for critical measurements such as
for expert opinions.
8.5.5 Minimum sensitivity
The minimum sensitivity of a measurement system can be estimated by considering the exposure
limit given as a radiant exposure (dose) and the expected exposure duration. The minimum
sensitivity in terms of measured irradiance is calculated by dividing the exposure limit by the
exposure duration. For instance, with an exposure limit of 30 J m -2 and an expected maximum
exposure duration of 8 hours, the minimal level of irradiance which can lead to exceeding the
exposure limit (and thus should be the sensitivity limit of the radiometer) is 10 -3 W m -2 (1 mW m -
2 , or 0.1 µW cm -2 ).
8.5.6 Dynamic range
Especially for spectroradiometers, a large dynamic range is often necessary for accurate
measurements, especially when there is a weak source emission in the UVC/UVB region and a
strong emission in the UVA region, as the action spectrum is dominant in the UVC/UVB and the
UVA region contributes relatively little to the effective irradiance.
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