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 effect.

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.

This additives find ready acceptance in Detergents, manufacturing of paper. This results in white paper and clothing being shown up as fluorescent under illumination of UV. They are able to enhance the colour of clothing. Besides this the other applications are in adhesives, non-destructive testing of metal parts and other fields.

• They are not readily biodegradable.
• Can cause allergic reactions.
• Toxic for fishes if discharged in waters.