These are the Colours Your Eyes Can’t See

It is easy to assume the spectrum of colours we see contains all the colours that exist in the world. In one way, this is true – that is, it contains all the colours that exist in the human world. But in reality, there are a huge number of other colours that are simply not perceptible to the human eye-the colours our eyes can’t see.

The colours we perceive are the result of how our brains – with the help of our eyes – interpret light rays across the electromagnetic spectrum – minute energy packets radiating at varying frequencies in a wave motion. Of course, that all sounds a bit complicated, doesn’t it?

What we really need to know is that our eyes can only interpret a limited range of these light rays. This means that there are a range of colours we can’t see – this phenomenon is known as the “opponent process” and the colours our eyes can’t see are called “forbidden” or “impossible” colours.

How Do We See Colour?

Our vision works by picking up the light that bounces off of objects around us. This light enters the eye through the cornea and the pupil. The cornea (the transparent outer layer) bends the light into the eye while the pupil dilates or constricts to let in more or less light.

The refracted light is directed towards the retina at the back of the eye. The retina is made up of millions of photosensitive cells known as cones and rods which are responsible for detecting light and sending information to the brain via the optic nerve. Rods are responsible for our perception of light and dark and our peripheral vision; cones are what allow us to perceive colour.

There are three types of cones, each of which is sensitive to a different range of light waves. Humans have more cones that are sensitive to red light than any other type, which means our vision is more suited for warmer colours such as reds, yellows, and oranges. Our cones are limited to perceiving light waves that fall within the range of 400 nanometres and 700 nanometres.

For example, the wavelength of a gamma ray is about the length of the nucleus of an atom – which is much too short for our cones to pick up. At the other end of the spectrum, radio waves are too long at the length of two Empire State buildings stacked one on top of the other!

Other animals have different kinds of cones that allow them to pick up a different range of colours on the electromagnetic spectrum. For example, dogs are more limited in the wavelengths their cones can perceive which means they can see a more limited range of colours. On the other hand, butterflies can see ultraviolet light that humans are unable to detect. Interestingly, the prize for most types of cones goes to the mantis shrimp, with an impressive 12 different kinds!

The Opponent Process

According to the “opponent process” theory, the colours we see can be paired into opposing hues. When we perceive these opposing colours (for example, green and red), they cancel each other out. This limitation means that some colours are simply imperceptible to the human eye.

Some vision experts argue that these so-called “impossible” colours are simply intermediary colours between two colours we can see. Nonetheless, experiments have demonstrated that some of these colours have been seen. Impossible colours may not exist as individual colours like red, blue, and green. Still, various studies have now demonstrated that the brain can be “tricked” into seeing something unfamiliar and appreciating a wider spectrum of colour than we thought was possible.

The impossible Colours

Now, let’s take a closer look at these so-called “impossible colours”. As we mentioned earlier, humans have three types of cones that allow us to see a certain range of light, and therefore colour, on the electromagnetic spectrum. These colours are blue, green, and red.

However, we are obviously able to see much more than these three colours. That’s because there is often an overlap in the wavelengths of these three colours, resulting in a much wider range. For example, white is not a wavelength of light, but rather a mixture of different colours.

The antagonistic way in which colours are presented and the opponent process we mentioned earlier means that our eyes are unable to detect certain colours at the same time. These are light vs dark, red vs green, and blue vs yellow. That’s why – if you have blonde hair, you might be told to use purple shampoo to banish yellow tones in your hair!

The opponent process theory was developed in the 1970s. It suggests that it is impossible for humans to perceive the so-called impossible colours. However, since its origin, a number of studies – starting with a famous 1980s experiment – have claimed that it is possible to “trick” the brain into seeing these colours.

This experiment – which it is not recommended you try at home – involved subjects staring at an image made up of two strips: one red and one green. The subjects’ heads were stabilised with a chin rest and their eye movements were tracked using a camera. The images moved with their eye movements to ensure their eyes remained fixed on the opposing colours and they received a continuous wavelength of light.

The results of the experiment suggested that, in the right conditions, the border between the two opposing colours seemed to gradually dissolve, allowing participants to see the impossible colours between them!

With over two million working parts, our complex eyes allow us to see a vast range of colour – so many that it can be impossible to imagine that there could be more. And yet, a day in the life of a mantis shrimp would certainly open our eyes to just how colourful the world can be.

Colour perception isn’t the only way to improve your vision. If you’d like to learn more about Laser Eye Surgery, get in touch with one of our friendly clinic coordinators or Book a Consultation today!