White's illusion is an optical illusion illustrating the fact that the same target luminance can elicit different perceptions of brightness in different contexts. An optical illusion is any illusion that deceives the human visual system into perceiving something that is not present or incorrectly perceiving what is present. ... The word luminance, a synonym for luminosity, means emitting or reflecting light. ... Brightness is an attribute of visual perception in which a source appears to emit a given amount of light. ...

Note, that although the gray rectangles are all of equal luminance, the ones sharing a longer border with the lighter context appear brighter than the ones sharing their longest sides with the darker context. The word luminance, a synonym for luminosity, means emitting or reflecting light. ...

Television screens depend on this visual illusion. Pixels that are not illuminated are seen as black, when they are really the same dim gray seen when the television is turned off. A pixel (a portmanteau of picture element) is one of the many tiny dots that make up the representation of a picture in a computers memory. ...

Whites illusion illustrates the fact that target luminance can elicit different perceptions of brightness in different contexts. ...