Optical Illusions

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About this simulation

24 classic optical illusions for the whole class. Pick one, ask the question, then press Show the truth: lines that are the same length, greys that match, a triangle that is not there and pictures that seem to move.

What students can explore

Which red line is longer: the top one or the bottom one?
Which square is darker: A or B?
Can you see a bright white triangle? Can you see its edges?
Stare at the cross on the bee. When the picture turns white, keep looking. What colour is the bee now?
Which square is at the front of the cube? Keep looking. Does it change?

Learning objectives

1Notice that what we see is built by the brain, not copied from the eye like a photo.
2Test an illusion by measuring, comparing or changing it, instead of trusting a first look.
3Explain in simple words why size, light, colour and movement can fool us.

Questions teachers ask

Why do optical illusions happen?

Your brain does not see the world like a camera. It uses shortcuts and guesses about distance, light and movement. These guesses are usually right, but an illusion is a picture that makes a shortcut give the wrong answer.

How can I use optical illusions in class?

Pick an illusion and show it to everyone. Ask the question and let students vote. Then press Show the truth and read why it happens together. Many illusions also have a strength slider: slide it to 0 and the trick disappears.

Are the moving illusions safe to show?

Nothing flashes. The moving pictures can be paused, and the staring activities only start when you press the button. If anyone feels dizzy, they should look away and rest their eyes.

Embed this simulation

Drop it into your LMS, blog, or class site — free.

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