The invention relates to a method and an apparatus for recognizing forged documents of value, wherein the documents of value are illuminated with clocked excitation light of a light source. Within the bright phase of the excitation light a first luminescence intensity is detected, within the dark phase a second luminescence intensity. Because of the afterglow of the light pulses there is a residual fluorescence, which distorts the luminescence intensity in the dark phase. By linking the second luminescence intensity with the first luminescence intensity, e.g. by subtracting a scaled first luminescence intensity, a corrected second luminescence intensity is determined, which substantially corresponds to the phosphorescence signal of the document of value.