Adelson's Checker Shadow Illusion

Adelson's Checker Shadow Illusion demonstrates how our visual perception can be fooled by context. In the illusion, a checkerboard pattern has a shadow cast over part of it, making some squares appear darker or lighter than they truly are. Surprisingly, two identical gray squares—one in the shadow and one outside—look different in color because our brain interprets the shadow as affecting the brightness. This shows that our perception of color and brightness is influenced by surrounding cues and assumptions about lighting, rather than solely by the actual luminance of the objects.