Optical brighteners, or optical brightening agents, as they are known are the types of dyes that shows the capacity to absorb light in the violet and ultraviolet region of the electromagnetic spectrum. Subsequently they re-emit light in the blue region.
Primarily these additives are employed to enhancing looks of colours in
fabrics or papers. They can easily enhance the appearance of white
things. The most popular class of chemicals that displays this property
are the stilbenes. Others include derivatives of pyrazolin, cumarin,
benzoxazol, naphthalimide and pyrene. Optical brighteners have
effectively replaced blues that was earlier used to produce the same
Though the exact number of Optical brighteners are not known the Colour
Index lists around 350. Some of the optical brighteners according to CI
are Fluorescent Brightener 220, CI Fluorescent Brightener 260.