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.
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.
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.
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.
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.
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.