Optical illusion: Is square B lighter or the same colour as that of A?

The optical illusion showcase a checkerboard with light and dark squares. It is partly shadowed by another object.

Optical illusions have been around us forever and are fun and engrossing, and they challenge our eyes and brain to see something that differs from reality. Case in point, this famous checker shadow illusion. The illusion depicts a checkerboard with light and dark squares, partly shadowed by another object. You need to figure out whether square B is lighter or the same colour as that of A.

The optical illusion shows a checkerboard with light and dark squares, partly shadowed by another object. (Persci)

The famous illusion was created by Edward H. Adelson in 1995 and was shared on the website of the Perceptual Science Group of the Department of Brain and Cognitive Sciences at MIT.

Take a look at the optical illusion image below:

Optical illusion created by Edward H. Adelson in 1995. (Persci)

Does square B appear lighter or the same colour as that of A? Well, you might say that square B is lighter than square A. However, that's not the case, as the squares are of identical brightness.

For those who are looking for an explanation, here is an image that might help:

Checker shadow illusion with explanation.  (Persci)

The image shows two stripes with the same shade of grey joining the squares marked A and B. Thus, it becomes evident that the colour of both the squares are same. The illusion is related to the famous cornsweet illusion and tricks us each time we look at it.