Significant increase of the previtamin D cis-trans isomerization efficiency with increased concentration of initial provitamin D was observed in both nematic and cholesteric LCs at room temperature, but the effect revealed reduced progressively with heating, and in isotropic phase it disappeared. The results obtained indicate on the collective character of cis-trans isomerization in liquid crystals due to the ordering of LCs. Here we present our results on the dynamics of the cholesteric phase induction and its propagation in response to the UV-induced geometry change of the provitamin D dopant molecule.