Brightness, Whiteness and Colour Brightness is defined as the percentage reflectance of blue light only at a wave length of 457 milli microns. Whiteness refers to the extent that paper diffusely reflects light of all wave lengths throughout the visible spectrum. Whiteness is an appearance term. Colour is an aesthetic value. Colour may appear different when viewed under a different light source. Brighness is an arbitrarily defined, but carefully standardised, blue reflectance that is used throughout the pulp and paper industry for the control of mill processes and in certain types of research and development programs. Brightness is not whiteness. However, the brightness values of the pulps and pigments going into the paper provide an excellent measure of the maximum whiteness that can be achieved with proper tinting.

The colour of paper, like of other materials, depends in a complicated way on the characteristics of the observer and a number of physical factors such as the spectral energy distribution of the illuminant, the geometry of illuminating and viewing, the nature and extent of the surround and the optical characteristics of the paper itself.