Brightness Constancy

Also called Lightness Constancy its when we perceive an object as having a constant lightness even while its illumination varies. This depends on the relative luminescence or the amount of light an object reflects relative to its surroundings. One example would be a piece of paper under a bright light verses the same paper under a dimmer light. Our eyes perceive the paper as being lighter with the bright light than in the dimmer light but based on our knowledge we know the white paper is always white no matter how dark or light it is.