Colour and Colours

Colour and Colours
19 January, 2023

We are in a world where colours dominate our lives, from reading signs on the road to seeing if the fruit is ripe to eat. It affects our moods - blue is calming - red can make us tense.

We use and experience colours every day in our lives without even appreciating them.

What is colour?

Colour is simply light of different wavelengths and frequencies and light is just one form of energy that we can actually see that is made up of photons.
We are all surrounded by electromagnetic waves of energy of which colour is just a tiny part.

The visible spectrum of colour as we see it, consists of seven main colours:

The retinas in our eyes though have three types of colour receptors in the form of cones. We can actually only detect three of these visible colours - red - blue and green. These colours are called additive primaries. It is these three colours that are mixed in our brain to create all of the other colours we see... how clever we are! The wavelength and frequency of light we see, also influence the colour we see. The seven colours of the spectrum all have varying wavelengths and frequencies. Red is at the lower end of the spectrum and has a higher wavelength but lower frequency than Violet at the top end of the spectrum which has a lower wavelength and higher frequency.

Where does colour come from?

Colour simply comes from light.

The prism

To physically see this, we need a prism. When light from the sun passes through a prism, the light is split into the seven visible colours by refraction. Refraction is caused by the change in speed experienced by a wave of light when it changes medium.

Light energy

The amount of energy in a given light wave is proportionally related to its frequency, thus a high-frequency light wave has a higher energy than that a low-frequency light wave.

Colour is made up of different Wavelengths and Frequencies

Each colour has its own particular wavelength and frequency. Each colour can be measured in units of cycles or waves per second.
If we can imagine light travelling in waves like that in an ocean, it is these waves that have the properties of wavelength and frequency.
A wavelength is a distance between the same locations on adjacent waves. As an example; an ocean full of waves, that were 10 meters apart, could be said, to have a wavelength of 10, whereas an ocean of waves that were 30 meters apart would be said to have a wavelength of 30. The same applies to light. The colour RED has a wavelength of around 700 nanometers long - one wave spans only 7 ten millionths of a meter! Violet has a much shorter wavelength, so each violet wave would span a much shorter distance.