Explore the Screen

Try this, in order

1. Start: three big stripes, swapping colours once a second. Easy to follow.
2. Slide Subdivide up a few steps. The stripes break into smaller and smaller rectangles, like the screen is growing its own pixels.
3. Now push Speed up. Once the lights are tiny and swapping fast, your eyes give up trying to follow each one... and the whole thing starts to look pale, washed out, almost white.
4. Tick "Compare with the real colour". A circle of the genuine mixed colour appears in the middle. How close is the illusion? Step back from the screen, or squint, and watch them merge.
5. Now pick a colour. Try orange. Watch what the lights do: the red ones stay bright, the green ones go dimmer, and the blue ones switch off completely. Step back... orange. No orange light anywhere on the screen, ever.

The three modes

• Take turns: every light keeps its own colour, and only one colour is switched on at a time: all the reds, then all the greens, then all the blues. Every spot on the screen is actually dark two thirds of the time, but your eye never notices. Old projectors really worked this way, with a spinning colour wheel. Notice the "white" it makes is dimmer, because the lights spend most of their time off.
• Swap: every light stays on and they pass the three colours around. The brightest blend, and both tricks at once.
• Steady: nothing flashes at all. Red, green and blue just sit side by side, and it STILL turns white when the lights are small enough. This is exactly, literally, what your real screen is doing right now: no flashing needed, just three tiny lights too close together to tell apart.

What's the trick?

There is no white light coming from this page at all, only red, green and blue taking turns. Two things blend them together:

• Your eyes are slow. They hold onto what they just saw for a fraction of a second (this is called persistence of vision). If red, green and blue arrive in the same spot fast enough, your brain averages them into one colour: white.
• Your eyes are blurry at a distance. When the lights get tiny, side-by-side red, green and blue smear together into a single dot, even without any flashing. That's why stepping back makes it whiter.

Here's the punchline: your screen is doing this trick right now. Every single "white" pixel on this page is really three microscopic lights (one red, one green, one blue) sitting so close together that your eyes cannot tell them apart. If you have a magnifying glass or a drop of water on an old monitor (ask first!), you can actually see them.

Any colour, three dimmer switches

The colour picker shows the deepest part of the trick: the lights never change colour, they only change brightness. Pick orange (#FF8800) and the red lights run at full power (FF), the green lights at just over half (88), and the blue lights turn off (00). Your eye blends those brightnesses into orange, even though there is no orange light anywhere. Every colour you have ever seen on a screen, every photo, every game, every skin tone, is just these three dimmer switches.

Challenge questions

• What's the smallest speed that still looks whitish when Subdivide is at maximum? Why does it need less speed when the lights are smaller?
• Why does the illusion get stronger when you walk to the back of the room?
• TVs used to draw their whole picture as flashes like this, 50 times every second. Why did nobody notice the flashing?

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