Adelson’s Checkershadow Illusion 1/52


52 weeks 52 different Optical Illusions

I love optical illusions so i thought i would share a few of my favorite and with many people opting to take up 365 day challenges i thought i would try a 52 week challenge in which i will share with you a different Illusion every week. so if you have any you would like me to feature get in touch.


Week 1 the classic Adelsons Checkershadow Illusion

INSTRUCTIONS - Look at the two target squares labelled "A" and "B".

Is one darker than the other? watch the GIF animation above

EFFECT - The tile labelled "A" appears significantly darker than the tile labelled "B".

But in fact they are both the same shade of grey.

Don’t believe me check out the video below…


Below you can find an extract from an article from Illusion Index which goes into the complexities to why this illusion works the way it does.

Adelson’s Checkershadow Illusion

Adelson’s Checkers Shadow illusion exploits the mechanisms underlying lightness constancy: our capacity to perceive the lightness (or reflectance) of a surface as invariant, even when the intensity of incident light (the illuminance) is changing at a point or is variable across the surface. Under normal circumstances, lightness constancy allows us to distinguish between brightly lit dark surfaces and dimly lit white surfaces, which helps us to detect edges and forms. It is just one of a number of constancies – including size, shape, colour and roughness – that humans exhibit that are used to allow us to skillfully negotiate our environment. In the general case, perceptual constancy is defined as a subject’s capacity to perceive some property of an object (e.g. lightness, colour, size) as being independent of external conditions (e.g. lighting or distance) (Gilchrist 2010).



Thomson, G. and Macpherson, F. (July 2017), "Adelson's checker-shadow illusion" in F. Macpherson (ed.), The Illusions Index. Retrieved from