Visual contrast
Visible fluorescence is stimulated in certain trace materials using narrow-band visible light. Differently coloured sources are
available to suit the type of trace deposit sought. The longer wavelength fluorescence must be viewed using a suitable
longpass filter.
Anti-Stokes fluorescence
Anti-Stokes fluorescence or IR Fluorescence 840-1100nm occurs in certain types of security inks and pigments. The process
differs from normal fluorescence in that the emission undergoes an anti-Stokes shift to a wavelength shorter than the excitation
radiation (i.e. a colour shift away from the excitation light, towards the blue end of the spectrum).
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