A rotating band shadow meter will give you the diffuse radiance as well as direct radiance. When the band is in the lower location the sensor will measure all the radiance from the sun both direct and indirect. when the band is raised it blocks the direct sun into the sensor giving an indirect radiance measurement. The total radiance - the indirect radiance will give you direct radiance. In this case the meter is setup to capture the UV portion of the spectrum. Multifilter suggests that it can record radiance for bands of UV radiance so it would be tracking radiance on two or more ranges wavelengths. The model described in this link supports six distinct frequencies though none are in the UV band.
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