Brightness and Darkness as Perceptual Dimensions
Figure 1
Brightness and Darkness Induction
Viewed from left to right, the grey disks appear to vary from dark to bright, even though they share the same luminance value. This induction effect arises because the background luminance varies along a gradient, leading to a change in the polarity and magnitude of contrasts formed against the disks. Brightness refers to the perceived luminance, or grey shade, of the disk when the luminance of the disk is greater than that of the background. Conversely, darkness is defined as the perceived luminance of the disk when the luminance of the disk is less than that of the background. The conventional way of thinking about this perceptual effect is that darkness is simply the negative of brightness, meaning that all the grey shades above are contained in a 1-D continuum, like real numbers along a number line.