Perception Deception

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When you use this hands-on exhibit…you’ll see a circle of ping pong balls illuminated by LEDs (light emitting diodes) so they look ‘yellowish’.

The middle ping pong ball contains pure yellow LEDs, while ping pong balls in the surrounding circle have different proportions of red and green LEDs to give yellowish coloured light.

You need to choose the ping pong ball in the circle that most closely matches the yellow ball in the centre.

However, you may find that your friends or family do not agree on which pair matches best!

If you’re arguing about a paint colour, don’t blame the paint company!

Blame genetics and perception.

We all differ in our colour perception, thanks to differences in our genes and trichromacy, which is the technique humans use to perceive millions of colours.

Light receptors (or cones) in your eyes detect certain wavelengths of light and generate colour responses in your brain. So your brain ‘sees’ or perceives colour rather than your eyes.

Now you may assume that you’ve got a huge range of cones for all the colours in the world, but your eyes can only actually detect three wavelengths of light:

• Light at around 480 nanometres is seen as ‘violet’ by your brain (detected by short or S-cones in your eyes).
• Light at around 530 nanometres is seen as ‘green’ by your brain (detected by medium or M-cones).
• Light at around 650 nanometres is seen as ‘red’ by your brain (detected by long or L-cones).

Hang on! You can see so many more colours than just red, green and violet.

And there are no ‘yellow’ cones, so what happens when you see yellow?

Light at 570 nm is interpreted by your brain as ‘yellow’ and mixing red and green spotlights creates light which your brain also interprets as yellow.

Your cones which respond to 530nm (‘green’) and 650 nm (‘red’) wavelengths of light are both being stimulated when you see 570 nm light.

Your brain combines the nerve signals from these two sets of cones and you perceive yellow.

The light itself doesn’t change, but your brain processes the information differently so you perceive colour.

But our genes play a role in how we see colour too.

Because we all have slightly different genes, we also have slightly different amino acids called photo pigments in our cones. This tiny molecular difference produces difference in colour perception between people.

Some people are more sensitive to 650 nm (‘red’) light, while others are more sensitive to 530 nm (‘green’) light. This affects how they perceive yellow coloured lights that are created with a mixture of red and green light.