Seeing the Light: Perception and Discrimination of Illumination Color

The contributions of surface reflectance and incident illumination are entangled in the light reflected to the eye. Historically, the extent to which the perception of one determines the other has long been debated, particularly in empirical studies of surface lightness and color constancy. Despite enormous progress in physical measurements of the spatial, spectral, and temporal properties of natural illumination, and in the ability to generate and control in real time artificial light of an almost infinite variety of spectra, the questions of whether and how people perceive the illumination as a distinct entity with its own color, and the interdependence of perceived surface color on perceived illumination, remain open. Given the rise in novel lighting interventions that modulate illumination spectra in order to improve health, well-being, productivity, and culture, it has become increasingly important to understand the two-way interaction between the visual and nonvisual sensing of illumination.