A sensor for checking value documents has an illumination device for illuminating a value document, an imaging optic and a detection device. A light source receiver has at least two light sources which have mutually different emission spectra. The illumination device contains a microlens array which contains a multiplicity of microlenses, which with the light source receiver are arranged such that each of the light sources arranged on the light source receiver has exactly one of the microlenses associated therewith.