Brightness illusions
Identical greys that look different, ghost spots that flash and edges that repaint whole surfaces.
Brightness illusionsHermann GridGrey smudges flicker at the crossings of a black-and-white grid.
Brightness illusionsScintillating GridWhite dots on a grey grid seem to flash with black spots.
InteractiveBrightness illusionsCheckerboard Shadow IllusionA dark square in light and a light square in shadow are the same grey.
InteractiveBrightness illusionsSimultaneous ContrastA uniform grey bar looks lighter on the left and darker on the right.
InteractiveBrightness illusionsCornsweet IllusionLeft and right halves are the same grey, but the left looks lighter.Advertisement
Why grey is never just grey
Your eyes are not light meters. They report differences, edges and surfaces, and they discount lighting so that a white page looks white in shade or sun. Brightness illusions catch that system in the act: identical greys look different, edges repaint whole regions and grids sprout spots that are not there.