Chevreul Illusion
Experience the 'staircase' of gray that appears to have non-existent curves.
🧐 What do you see?▼
Observe the horizontal bands of gray. Each band contains a single, solid color. However, you likely see a "fluted" effect: the side of a band touching a darker neighbor looks lighter, and the side touching a lighter neighbor looks darker.
🧠 Why this works▼
Discovered by chemist Michel Eugène Chevreul, this is a form ofSimultaneous Brightness Contrast. It's essentially the same underlying mechanism as Mach Bands, but it occurs on discrete steps rather than a smooth gradient.
Your brain is optimized to find edges. By darkening one side of a boundary and lightening the other, it makes the "step" between colors much more obvious than it actually is. This helps you identify distinct objects in complex visual scenes.
🧪 Try variations▼
- Vary Intensity: This changes the number of steps. More steps usually result in a more convincing "curved" or 3D appearance.
- Pause to Verify: Hit Pause to see red divider lines. Cover the gap between them to see that each color is actually perfectly flat.
❓ FAQ▼
Is this why painting walls is hard?
Yes! Painters often struggle with this when painting adjacent walls different shades of gray—the corner can look like it has a glowing line or a deep shadow even when the paint is flat.