Colour #2: The Electromagnetic Spectrum

Colour starts as light

Our senses are our way of perceiving the world around us. Some senses are tuned to detect big organic molecules, like smell. The sour receptors in your tongue detect hydrogen ions, arguably some of the smaller things that exist.

Your eyes detect photons, which are the most fundamental particles in the universe, and which are what light is made of! They are the only things that can travel at light speed (hence the name), and they have zero mass. Fascinating things!

The sun happens to emit a literal bajillion of them every second, and they love bouncing off of things, which is why many animals have evolved eyes to catch them.

There are many kinds of light

Photons are traveling in a wave motion, and how fast the wave oscillates is called a photon’s frequency (measured in Terahertz, THz). The higher the frequency, the more energy each photon has, and the shorter the wavelength (measured in nanomenters, nm), which is the distance between two peaks of the wave.

Our eyes can only detect a very small range of frequencies, which we call the visible spectrum. The rest of the electromagnetic spectrum is invisible to us, but it is still light! When you microwave your food, or when you listen to the radio, get an X-Ray, or when you use your phone’s Wi-Fi — it’s all just photons.

You might have heard stories of people’s organs literally melting after being exposed to radioactive gamma rays, because the photons are so high in energy that they are ripping your cells apart — it’s safe to say that evolution hasn’t really equipped us to deal with that part of the spectrum. However, it’s probably good that our eyes aren’t able to detect the low-energy radio waves, because if they could, we’d be constantly blinded by the Wi-Fi signals in our homes.

The visible spectrum is the rainbow

The tiny sliver of light our eyes can detect is called the visible spectrum, and it contains all the colors of the rainbow. You may remember the mnemonic ROYGBIV: Red, Orange, Yellow, Green, Blue, Indigo, Violet.

Exact boundaries between visible and invisible light are a little fuzzy and vary from person to person, but on the ends of the visible spectrum you will see light slowly fade into infrared and ultraviolet and out of sight.

A bunch of nerds called the International Commission on Illumination (CIE) define what’s called the “CIE standard observer”, a hypothetical person with perfectly average eyes, and they have run tests on people in the 360-830 nanometers range. The parts of the spectrum that are visible well for most however is probably closer to like 380-750 nanometers.

Where is pink?

You might notice a strange absence of pink in the visible spectrum. Last I checked it’s a color that exists, so where is it?

And also, do you notice how like red, yellow, and green take up a lot of the visible spectrum, but blue and violet get a comparatively small share? Why is that?

Well, the answer is that colors are basically hallucinations of our brain and pink isn’t real, and our eyes are bad sensors shaped by evolution!

Well no that’s a bit overdramatic. But stay tuned for next posts, where we will explore the human visual system, to answer all those questions and more!