System and method of improving the signal to noise ratio of bar code and indicia scanners that utilize fluorescent inks

Abstract From the Canadian patent

A bar code and/or indicia scanning method that is able to determine what light was emitted from an upper layer invisible bar code and/or upper layer invisible indicia and what light was reflected back to the detector from avisible lower layer bar code and/or visible lower layer indicia. The detecting is "blind" to the spectra of the excitation source. Rather than differentiate between the exciter and emitter in the spectral domain this invention, differentiates between the exciter and the emitter in the time domain. The latency and persistence of the phosphorescent pigments of the invisible ink are used so that the detected signal is only the signal emitted by the upper layer invisible ink …