Fluorescence emission of guest molecules in cholesteric liquid crystal hosts was modulated by an electric‐field‐induced cholesteric‐nematic transition. The contrast ratio between the two states can be greater than 15, and is affected primarily by the scatteringproperties of the phase and the order parameter of the guest. Data are presented on the dependence of the contrast ratio on the cell parameters and the structure of both guest and host. A simple model is presented accounting for the observed behavior.
