Brightness is measured as reflectance in the blue portion of the visible spectrum.
Complete reflectance provides a white color.
Absorption of any part of the visible spectrum by a material will result in the perception of color by the eye. Bleached kraft has brightness values ranging from 86-94. Source of Dark Pulps . Polysaccharides do not absorb light in the visible range and therefore a pulp composed solely of cellulose and hemicellulose should be white. Methods for Improving Brightness .