A chemical substance used to increase the apparent whiteness of paper. Also used in printing coatings to give the finished product a whiter appearance.The chemical substance reflects ultraviolet light in the blue end of the visible spectrum, thus increasing the amount of visible light reflected. Papers containing optical brightners will appear different under daylight, flourescent or incandescent light.
Optical brighteners are chemical substances which increase the apparent whiteness of the paper, by reflecting ultra-violet light in the blue end of the visible spectrum, which increases the amount of visible light reflected causing the brightness of the sheet to be increased.
A class of widely varying types of chemical compounds with one common characteristic, they absorb ultraviolet light and re-emit it as visible blue and violet wavelengths. Their presence in and on a substrate tends, therefore, to "whiten" it. They are also known as "fluorescent agents" because they strongly fluoresce under "black light" (U.V. light of longer wavelengths). Due to the fluorescent effect and re-emission of blue/violet visible light, optical brighteners add a "sparkle" or brilliance to some substrates in addition to their "whitening" effect.