Checker–shadow illusion

Slide the shadow strength to watch tiles A and B trade places

When a soft shadow sweeps across a checkerboard, identical tiles look wildly different. Start with the core control below, then scroll to unlock the full lab.

Live canvas

Step 1 · Shadow strength

Turn the cast shadow up or down

With no shadow the checkerboard is boringly balanced. Strengthen it and the square inside the shade suddenly appears darker than its twin outside, even though the pixels remain identical.

0.50×

Step 2 · Light direction

Rotate the light source around the board

The perceptual trick depends on a convincing light direction. Adjust the angle or set it spinning to see how the apparent “lighter” tile swaps places.

30°

Step 3 · Shadow shape

Control width, length, softness, and the casting object

A long, soft-edged shadow makes the comparison more ambiguous. Reveal the cylinder to drag it and test different radii.

260
560
60
80

Tip: drag the cylinder directly on the canvas; the shadow updates instantly.

Step 4 · Board and palette

Adjust the checkerboard itself

Once you believe the illusion, explore how board size and tile contrast change its potency. Strong contrast and a generous margin keep the comparison readable.

8
70
60
35%
70%

Step 5 · Proof tools

Fade the context and bridge the twins

Labels and reveals help you convince sceptical audiences. Fade the surroundings, lock the luminance equality, or draw a connecting strip to show the tiles really match.

0%
Prove they’re identical

Step 6 · Presets & export

Jump to favourite setups or save the canvas

Use curated presets for classroom demos, or export a PNG/SVG snapshot when you find a configuration that astonishes people.