The detector’s spectral response follows closely the erythema action
spectrum (Fig.1.)[1]. Due to built-in Teflon diffuser the detector
has negligible azimuthal error making the measurement insensitive to
the rotation of the detector. Extended measurement range of 600
MED/Hr enables measurement of intense radiation.
In conjunction with the Solar Simulator and XPS200 Xenon Lamp Power
Supply the PMA2100 with the PMA2103 detector can operate as a smart
dose ontroller/monitor substantially enhancing the functionality of
the Solar Simulator.
The measurement result can be shown in MED/Hr, µW/cm2 as well as a
time to accumulate 1 MED. The detector's high dynamic range allows
measurements down to 0.1 µW/cm2 with the ability to measure
radiation as strong as 3.5 mW/cm2.
The biologic effectiveness of ultraviolet radiation is strongest for
wavelengths between 280 to 320 nm, classified as UV-B by the CIE.
Several biologic action spectra, functions relating wavelength and
the biologic effectiveness, are shown in Figure 3. The most commonly
used, erythema action spectrum [1], also referred to as CIE 1987
action spectrum, represents the sensitivity of human skin to
sunburn.
Other biologic action spectra also exhibit rapid decline in UV
effect with an increase of wavelength over the UV-B range. In
general the reading of an erythemally weighted detector cannot be
directly interpreted as biological effectiveness other than
erythemal. However, there are ways to make the necessary correction
numerically [2].
The biologic effectiveness of the UV radiation can be measured in
terms of effective irradiance in radiometric units, for example
[µW/cm2]. It is often related to the sensitivity of the human skin
to sunburn and expressed in Minimal Erythemal Doses per Hour
[MED/Hr]. One MED/Hr is the effective irradiance capable of causing
minimum redness (erythema) in an average number 2 skin. Based on a
study [3], the relationship between MED/Hr and radiometric units was
determined to be:
1 [MED/Hr] = 5.83 [µW/cm2]
This formula is programmed into the PMA2103 detector allowing for
easy conversion of units. Consequently, the integrated effective
dose can be expressed in [mJoules/cm2] or MED.
Many sources produce UV radiation with a spectral irradiance
changing rapidly over narrow wavelengths range. Spectral irradiance
of the solar UV (Fig. 4) is an extreme example of such steep slope
due to the UV-B and UV-C absorbing ozone layer.


Figure 3: Selected Biologic Action Spectra |