The gray bars on the left look lighter than the gray bars on the right. They are identical.
Try this
- Tick Remove the stripes to check.
- Change Number of stripes: thin stripes give a strong effect.
Why it happens
This one breaks the simple contrast rule. The left bars border more white than black, so plain contrast would make them look darker, yet they look lighter. Michael White reported it in 1979. The leading explanations say the brain groups each gray bar with the stripe it seems to belong to, or treats the stripes as a transparent layer, and judges lightness within that group. It shows that how the brain organizes a scene matters as much as raw contrast.
Did you know?
The color version, where stripes of one color make the same red look orange or pink, is often called the Munker-White illusion.
References
- White M. (1979). A New Effect of Pattern on Perceived Lightness. Perception, 8, 413-416. doi:10.1068/p080413
- Anderson B. (1997). A Theory of Illusory Lightness and Transparency in Monocular and Binocular Images: The Role of Contour Junctions. Perception, 26, 419-453. doi:10.1068/p260419
- Background on Wikipedia
The illusion on this page is drawn by code written for this site. Last checked 1 November 2026.
Frequently asked questions
Why does White’s illusion work?
The brain groups each gray bar with the stripes it seems to lie on, and judges its lightness within that group.
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