Excessive UV doses have adverse effects on human health, but proper amount of UV is beneficial for people and is
essential in the natural production of vitamin D# in skin. Most of broadband UV-radiometers that have an output in
sunburn units are incapable to record correctly the vitamin D synthetic capacity of sunlight because of the difference
between the CIE erythema and 'Vitamin D synthesis' action spectra. The liquid-crystalline UV sensor based on
provitamin D photoconversions has been developed for direct observation of vitamin D synthesis under UV irradiation.
UV-induced transformation of provitamin D in cholesteric liquid-crystalline matrix is accompanied by the change of
cholesteric pitch value in the LC cell. The developed UV biosensor makes possible both instrumental and visual
monitoring of the vitamin D synthetic capacity of sunlight and/or artificial UV source.