Specularity,brightness, achromatic color—and orthogonality

For objects under the same illumination, the more specular object appeared brighter. This occurred irrespective of an object’s apparent achromatic color, the distance at which it was viewed, the level of illumination, the method used for collecting observations, and other conditions. Also, when identical specular objects were differently illuminated, the one under the higher illumination, with the higher maximal luminances, appeared brighter. In the five experiments, which involved 340 subjects subdivided into 17 groups, large fields of view and real spaces were used. The results supported the conclusion that apparent brightness and achromatic color are orthogonal phenomena, and that in four of these experiments increased apparent brightness was correlated to, if not determined by, maximal specular luminances without regard to achromatic colors and diffuse luminances. This conclusion was necessarily modified by a fifth experiment, which showed that if placed under sufficiently high levels of illumination, less specular surfaces appeared brighter than more specular surfaces. This was taken to mean that a total account of the apparent brightness of surfaces would depend on an undiscovered algorithm involving maximal specular and diffuseluminances and their areal extents. With regard to the validity of the studies, the subjects were shown to have phenomenally discriminated brightness from glossiness and glare. Finally, phenomenal gloss and glare were found to be correlated to a surface’s level of specularity.