We frequently encounter fluorescence in our daily lives. Fluorescent
lighting is widely used in public environments and fluorescent
paints are used to improve the visibility of traffic signs and
for attention-grabbing effects. Fluorescent dyes are also widely
used to alter or improve the appearance of paper products and
textiles. These special types of dyes are referred to as fluorescent
whiteness agents (FWAs) or optical brightening agents (OBAs)
and are specifically used to increase the whiteness of the products.
The latter application is a reason why FWAs can be found in
detergents. These dyes absorb ultraviolet (UV) light from the illumination
and emit light in the blue region of the visible spectrum.
In the paper industry, whiteness is a widely used quality parameter
of paper products and the whiteness value is an important sales
argument. To achieve higher whiteness levels, producers of paper
and board use more bleaching of the pulp and increased amounts
of FWA added in the papermaking process. Paper products with
a slightly bluish shade are perceived as being whiter than papers
having a more neutral color by most humans [1]. Therefore, the
addition of FWAs increases the perceived whiteness by increasing
both the lightness and the bluishness of the paper. Among the
many whiteness formulas proposed, the CIE Whiteness formula
[2] is the most widely used for paper products. This formula does
also reward slightly bluish papers and most commercially available
printing papers contain FWAs. To accurately measure flu