Z% Brightness - an01_97b Follow

Z% Brightness is a single-number index that is used to measure the brightness of white materials that tend to yellow with age and/or degradation. This index is not recognized in a formal test method. It is most often used as an in-house test method by companies in the paper industry. It may be used in quantifying optical brightening effects when a sample is measured with the instrument's UV filter in and then its UV filter out. It is sometimes used to measure the effectiveness of bleaching.

Conditions for Measurement
Instrumental: Any HunterLab color measurement instrument
Illuminant: Usually C, but others may be used
Standard Observer Function: Usually 2 degree
Transmittance and/or Reflectance: Reflectance.

Formulas
Z% is the CIE Z value divided by Z for the top of scale and multiplied by 100 to yield a percentage.

(formula)

Typical Applications
This index is used mainly in the paper industry, but it may be used on any white product that yellows.

(See attached pdf file for the complete article and formulas)