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

Abstract

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 a visible 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 after the light source is turned off. Illumination and detection are synchronized to reduce the effects of reflection to zero so that the detector need not be chosen to be blind to the exciter. The foregoing is particularly suited to LED and laser illumination where the light source may be easily turned on and off.

Dependencies are inferred from the claim text.