chapter  2
Visible characteristics of lighting
Pages 88

Visual constancy requires that we are able to differentiate between changes of surface lightness and surface illuminance. According to the ‘modes of appearance ’ model, ‘things’ that are perceived in surface or volume object modes have the attribute of lightness but not brightness. Helmholtz’s paper appeared white and the lump of coal black regardless of their relative luminances. Nonetheless, he would have been conscious that the coal was more brightly lit than the paper. While he perceived the stable attributes of these objects in surface mode, he would have perceived the different attributes of their lighting in localized illumination mode. While a luminance meter would measure the combined effects of illumination and surface lightness, a human observer assesses these independently. This chapter examines perceived attributes of lighting.