Evaluative Scale
Mathematical models developed by the Commission Internationale de l’Éclairage provide a multi-wavelength assessment of overall paper lightness and tint across the entire visible spectrum. This numerical system, known as cie whiteness, utilizes a single index to quantify the perceived whiteness of paper under specified illumination conditions. Standard papers without optical brighteners typically register values between seventy and eighty on this scale.
The formulation incorporates the human visual response to reflectance across multiple visual channels. It establishes a baseline where higher numbers indicate a closer approximation to an ideal diffuse white reflector.
Visual Concordance
Perception of clean paper by the human eye depends heavily on the presence of bluish tints that offset natural yellow wood fibers. Although traditional brightness measurements focus narrowly on a single blue wavelength, cie whiteness incorporates the green and red regions of the spectrum to align more closely with consumer judgments. This multidimensional approach ensures that papers with similar brightness but different tints are ordered correctly according to human preference.
High values require a carefully balanced addition of dyes and optical brightening agents during the papermaking process. If the tint departs too far toward green or red, the formula penalizes the score to match the negative visual impression.
Spectral Bias
Excessive addition of optical brighteners can cause a shift in the perceived shade that undermines the accuracy of the index. When the tint value exceeds the allowable limits of the cie whiteness equation, the resulting score becomes invalid because the paper appears distinctly violet or green. Standard procedures limit the applicability of the formula to samples that remain within these boundary conditions.
This restriction prevents manufacturers from inflating ratings through the uncontrolled loading of fluorescent additives.
