The Science of Colors

The Visible Spectrum of Colors

Did you know Magenta isn’t really a color? I did not, until recently. This and more when we have a look at the science behind colors.

The visible spectrum

Light makes up colors. Light — as a wave — has a wavelength and frequency. These wavelengths range from smaller than atoms to the size of galaxies and beyond. You’ll probably already know light in its many forms. We know the longest wavelengths as radio waves, and the smallest as gamma radiation. In between are other things, like visible light.

The wavelength ranges from large to small are:

  • Radio waves
  • Microwaves – yes, those that heat your food.
  • Infrared – night vision and TV remotes.
  • Visible light
  • Ultraviolet – only bees see.
  • X-rays – to look at your bones.
  • Gamma radiation – from nukes and reactors.

Today, we’ll only look at the visible light spectrum. Well, visible to us. As stated, bees can also see into the ultraviolet range. And snakes can ‘see’ infrared.

If you want to know more about gamma radiation, and radiation in general, go read my earlier article on that subject.

The visible spectrum ranges from around 400 nm (nanometer) to 700 nm. Of course, not all eyes are equal, so your mileage may vary. But, how do our eyes handle these colors?

Cones and rods

Light enters our eyes and the eye lens focuses it on our retina. Our retina contains two types of receptors. The rod receptors respond to luminosity, in other words, how bright the light is. The other receptor type, the cones, respond to color.

The reason for having two types is that the rods are more sensitive, but can’t detect color, and the cones can detect color, but not in dim light. If you’ve ever wondered why you can’t see color so well in dim light, this is the reason.

There are also three different types of cone receptors: short-wave, medium-wave, and long-wave cones. These three types respond differently to different parts of the visible spectrum. It’s a misconception that they only respond to certain colors. The three cone types respond to most of the visible spectrum, just in different amounts. The diagram below shows this.

So, how does our brain parse this data into colors?

Mixing colors

Our brain uses the input of the rods and cones to create our mental model of color. If you see a bright blue square, your rods will fire a signal, your S-cones as well, and your M- and L-cones only a little. As a result, your brain interprets this as bright blue. If the rods fire less, you’ll see dark blue. If the L-cones are firing, then you see red, and so on.

Before we circle back to magenta, we need to look at the difference between additive and subtractive colors

Additive and subtractive colors

So far, we’ve talked about light. Light creates what we call additive colors. When you combine red and green light, you get yellow, red and blue makes magenta, and so on. White color is, of course, a mix of the whole light spectrum. All your rods and cones fire equal signals and your brain says: white.

When you use paint, things work differently. This is because when we look at an object, we’re actually looking at light bouncing off of that object. When you shine white light on a blue ball, for example, you will see a blue ball. This is because the non-blue colors that fall on the ball are not reflected. It absorbs a part of the color spectrum of light.

When you start mixing things that absorb colors, they don’t start absorbing less, they naturally start absorbing more. So when you mix yellow paint with blue paint, you end up with green, where blue and green light would lead to yellow.

We’ve all been taught red-yellow-blue as ‘the’ primary colors in school, but this is really not true. At all. You’re really combining ‘a’ set of primary colors. In printing, CMYK (cyan-magenta-yellow-black) is more commonly used, because they lead to a wider range of colors when mixed. Different sets of colors are possible, as long as they can cover a large part of the color spectrum when mixed.

The color magenta

So, back to magenta. I told you it doesn’t really exist. Go have a look at the color spectrum at the top of this post.

See. It isn’t there, is it?

To create magenta with light, you combine red and blue light. When this reaches your eye, both your L-cones and S-cones fire a strong signal, but not your M-cones. This poses a problem for our brain.

As I described above, all additive colors combined add up to white. But your brain can’t interpret the red-blue combination as white, because the M-cones are not firing. They can’t see it as green either. Although green is between red and blue, it’s also the range of the M-cones, which again, are not firing a strong signal.

So, what does our brain do? It invents a color. And that color is magenta.

Mind blown.

Author: Martin Stellinga

I'm a science fiction and fantasy writer from the Netherlands