Irradiation illusion

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The irradiation illusion is an illusion of visual perception in which a light area of the visual field looks larger than an otherwise identical dark area. It was named by Hermann von Helmholtz around 1867;[1] but the illusion was familiar to scientists long before then; Galileo mentions it in his Dialogue Concerning the Two Chief World Systems.[2] It arises partly from scattering of light inside the eye. This has the effect of enlarging the image of a light area on the retina.


  1. ^ Hermann von Helmholtz, Handbook of Physiological Optics (J. P. C. Southall, Trans. 3rd ed.), New York (1910, 1962), Dover
  2. ^ Galileo Galilei, Dialogue Concerning the Two Chief World Systems (1632), Day 1.