Absolute brightness is defined as the reflectance of blue light with a specified spectral distribution peaking at 457 nm compared to that of a perfectly reflecting, perfectly diffusing surface. Although no physical material has such a surface, the discrepancies between a reference material and the perfect diffuser can be rigorously determined. Reference materials thus calibrated establish the scale of absolute brightness.
Bleaching agents strongly influence the reflectance of pulp in this portion of the spectrum. Absolute brightness is thus used to monitor bleaching action. The method is not intended to be solely definitive in the case of materials having a pronounced colour (Materials of pronounced colour should be measured for Visual Efficiency (Luminance Reflectance Factor, as measured with Technical Section, CPPA standard E.7P) or described in terms of CIE (International Commision on Illumination) colour coordinates as measured with Technical Section, CPPA standard E.5P.) or containing optical brighteners.
Since the method utilizes an integrating sphere geometry, it may be used with materials having relatively rough surfaces. The specular component is excluded. The use of relatively large sample aperture averages out point to point differences and minimizes the number of measurements necessary.
The testing and evaluation of a product against this method may require the use of materials and/or equipment that could be hazardous. This document does not purport to address all the safety aspects associated with its use. Anyone using this method has the responsibility to consult the appropriate authorities and to establish appropriate health and safety practices in conjunction with any existing applicable regulatory requirements prior to its use.
