How does the pen compare to other methods e.g. UV light detectors?
Under a UV lamp, the theory is that the cotton paper on which legitimate banknotes are printed should not fluoresce (i.e. is UV dull), while the paper available to counterfeiters contains brightening agents which give a characteristic blue glow. However, UV dull paper is easily available, any paper can be made UV dull by spraying it with readily available chemicals and UV dull cotton paper can become UV bright through contact, for instance, with recently washed clothing.
