: How does RGB work at the wave level?


I understand that light is simply electromagnetic waves that our eyes interpret as light.

And that RGB is a combination of red, green, and blue light.

But how does combining three separate lights actually result in a different color? Superimposing waves shouldn’t change the frequency/wavelength of the light at all, right? Is it just our eyes doing some black magic?

In: Physics

The short answer is it doesn’t. True yellow light has a wavelength of ~550nm. The “yellow” that your computer screen sends at you is just a combination of red (~700nm) and green (~520nm).

You’re correct that our eyes are doing black magic. We have three types of ~~light-sensing~~ (EDIT: color-sensing *) cells (called “cones”): L, M, and S, named based on what wavelength they’re sensitive to. (L is mostly sensitive to red, M mostly to green, S mostly to blue).

Colors like (true) yellow stimulate both the L and M cones, but our nervous systems can’t tell the difference between yellow and a mixture of red+green. That’s the fact that RGB displays leverage to their advantage.

Bonus fun fact: Magenta (red + blue) doesn’t correspond to any (pure) color, it’s just an invention of our brains to represent the L+S cones being stimulated at the same time.

Color only exists in our eyes. There are cells in your eye that react to different wavelengths. When one of the cells is activated, you see the corresponding color. When multiple cells of different types are activated, it makes you see a different color.

The specific color that you see isn’t an inherent property of the light wave. It’s a subjective experiences caused by the sensory cell triggering. Different wavelengths or combinations of wavelengths can trigger different clusters of cells, and thus look like different colors.