Your shadow is supposed to be a dark, flat version of you. On the RGB Wall, it’s blue. And red. And green. And pink. And yellow. All at once!
Raise an arm and it splits into a fan of coloured copies, each a different colour, each following you a beat behind. Nothing is drawn on the wall and nothing is projected onto you. These are your own shadows, and every one of them has colour.
What is the RGB Wall?
The RGB Wall is a shadow wall in the heart of London that turns the one thing you thought you knew about shadows on its head.
Three coloured lights, one red, one green, one blue, shine on a white wall from slightly different angles. On their own they’d blend into plain white light. Step in front of them and your body blocks each light from a slightly different spot, so instead of one dark shadow you throw several coloured ones. Move around and they stretch, overlap and mix into new colours in real time.
It reacts to everything you do, so no two people ever make the same shape twice.
The science behind it
This is additive colour mixing, the same principle behind every screen you own.
Red, Green, and Blue are the three primary colours of light. Mix all three at full strength and you get white, which is why the wall looks plain white before you step in front of it. Your phone and TV build every colour they show from these same three, by lighting up tiny red, green and blue dots in different amounts.
Now step in. Your body blocks the light, but here’s the twist: each of the three lights sits in a slightly different spot, so your body blocks each one from a different angle. Wherever you block the red light, that patch of wall still gets green and blue, which the eye reads as cyan. Block the blue, and you’re left with red and green, which reads as yellow. Block two lights at once and you get a shadow in the pure colour of whichever light is left. Every coloured shadow on the wall is a spot where you’ve blocked one colour of light and left the others to land.
Inspired by the Young–Helmholtz theory of trichromatic colour vision, developed by Thomas Young and later expanded by Hermann von Helmholtz
So your shadow isn’t really coloured at all. It’s a gap in one colour, filled by the rest. Want more of this? Our Science of Illusions page goes deeper.
The science behind it
Daylight and normal bulbs contain a broad range of wavelengths. When that light hits an object, some colours get absorbed and others bounce back to your eyes. A strawberry looks red because it reflects red light and soaks up the rest.
The Colourless Room is lit by low-pressure sodium light, the yellow-orange glow of old streetlamps. It’s almost perfectly monochromatic, giving off light at essentially one wavelength (around 589 nanometres). The light in the room only comes from a tiny part of the spectrum, so everything you see is just a brighter or darker version of that one tone.
Your eyes aren’t failing and your brain isn’t being fooled. Most of the colour information wasn’t present in the light reaching your eyes to begin with. That points to something stranger: colour isn’t really “in” objects at all. It’s in the light that hits them, and in how your brain reads what comes back. Change the light, and you change what information is reaching your eyes.
More of that thinking lives on our Science of Illusions page.
What to expect
The RGB Wall is a walk-up, hands-on space with nothing to press or queue for. Stand in front of it and start moving. Wave, jump, strike a pose, layer up with whoever you came with. The bigger and faster you move, the more dramatic the shadows.
Give it a minute, because the effect gets better the more you play with it. It’s part of your wider visit to Twist Museum, alongside 80+ interactive illusions, so there’s plenty more to explore once you’ve worn yourself out.
Photo and video tips
This one is made for video. Still photos are good, but movement is where the RGB Wall comes alive.
- Film in slow motion. A slow-mo jump or spin trails the coloured shadows behind you and looks incredible on a feed.
- Get someone to film while you move. The effect reads far better from a few steps back than it does from your own eyeline.
- Layer up with a friend. Two sets of shadows blending is more eye-catching than one, and it captures the reaction as well as the effect.
- Try a big, slow gesture. Arms wide, a slow kick, a spin. The clearer the shape, the cleaner the coloured trails.
Tag @twist_museum when you post. The RGB Wall is one of the most shared spots in the whole museum.
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