Figure 2: Transmission characteristics of optical filters used for discriminating UV-A and UV-B ranges. Filter characteristics for UV-A are shown by curve A (UFS-8, thickness 5 mm). For UV-B, a combination of two materials was used: UFS-2 with thickness of 2.5 mm (curve B1), ZhS-3 with thickness of 2.5 mm (curve B2). The curve B1 + B2 shows the transmission of the combined filter.