Phosphor bands were introduced on British stamps from 1959 as a replacement for the previous
graphite lined stamps 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 radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of the ...
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.
References
Postage stamps of the United Kingdom
Postal system of the United Kingdom
Philatelic terminology
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