Brightness Constancy
A sheet of white paper seen in the bright sunlight reflects a very different amount of light than the same sheet of paper seen later that night in a softly lighted room. Yet we perceive the paper as having the same whiteness in each case. This is an example of brightness constancy, our ability to see objects as continuing to have the same brightness even though light may change their immediate sensory properties. Psychologists have determined that an object will exhibit brightness constancy as long as both the object and its surroundings are in light of the same intensity. If the background brightness differs from the object, brightness constancy is not maintained. For example, if the background is lighter than the object, the object appears darker.