{{no footnotes, date=February 2012
Phosphor bands were introduced on British stamps from 1959 as a replacement for the previous
graphite lined stamp A graphite lined stamp is a postage stamp on which vertical lines of electro-conductive graphite are printed on the reverse. Graphite lined stamps were used in the United Kingdom from 1957 to 1960 as an experiment in the automation of mail sorting. ...
s as an aid in the mechanical sorting of mail.
The phosphor is applied in vertical bands, or more recently, all over the stamp, and fluoresces under
ultra-violet
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiatio ...
light. This enables the mail sorting machine to ''face'' the mail and sort it into types.
Phosphor is now widely used on stamps around the world. It is necessary to use either a short- or long-wave ultraviolet lamp to view the phosphor, according to the type of phosphor used on the stamp.