What is Color?

What is whiteness?

White is a color too. Although it is achromatic, it is still a color in the colorimetric sense. With an ideal white, all the incident light in the 400-700 nm range is reflected. This "ideal white" is, however, purely a theoretical quantity. Barium sulphate, which was once widely used as a white standard, "only" gives an average reflection of 98% across the visible spectrum.

"Whiteness that is, how white a material is is a yardstick for quality for many typically white materials such as paper or textiles. The "whiteness" of a material can admittedly come very close to an ideal white if the material is bleached, thus destroying the color pigments that absorb light. But if a white needs to be "bright" then optical brighteners are used to obtain a "perfect" white. These optical brighteners, which are also found in everyday life in washing powders and toothpastes, for example, have properties that enable them to absorb radiation in the UV range (<400 nm), which is not visible to humans, and then to release it again as additional light in the area of the spectrum that is visible to humans (> 400 nm). Materials that have been treated with an optical brightener can therefore have a reflection value of >100%. These materials appear to be "bright" white.