Glowing greys and surface-white: The photo-geometric factors of luminosity perception

The perception of luminosity is thought to depend upon the intensity of the stimulus: a surface begins to appear self-luminous when it emits or reflects a certain amount of light. This is known as the luminosity threshold. It is a common opinion among vision scientists that such a threshold is correlated to the intensity of a perceptually white surface, in the sense that only an area of the visual field with luminance higher than perceived surface-white will appear lumi- nous. Here we show grey colours that appear luminous in virtue of surrounding luminance ramps. These ramps are intended to mimic halos seen around light sources in natural environ- ments. The results of three experiments indicate that the phenomenon is in direct contradiction to the aforementioned assumptions and suggest the existence of separate perceptual pathways for self-luminosity perception and for surface-colour perception.