Almost all UV radiation (especially 240-280nm) is absorbed by Earth ozone layer, and the UV radiation that is created by some object near the Earth surface, can be detected only using special zone filters.

Crystal materials are robust substrates from which optical filters of high purity and optical homogeneity can be fabricated. Available crystalline materials: NiSO4*6H2O (NSH) and K2Ni(SO4)2*6H2O (KNSH).