Back to Basics: What Exactly is Colour?

Colour is derived from light, therefore in order for us to perceive colour there has to be a source of light. Natural light comes from the sun and is described as pure, white light; all other sources of light are man-made.


Light is in fact radiation in the form of electromagnetic vibrations from the sun, similar to the pulses of sound that come from hi-fi speakers. The human eye registers these waves of energy and the brain interprets the information as colour. 


We can only detect a limited range of these vibrations, known as the visible light spectrum, between wavelengths of 400–700 nanometres. The known electromagnetic spectrum ranges from 0.01 nanometres or less at one end of the scale (gamma rays), through to 0.1 metres or more at the other (radio waves).


The Effect of White Light Refracted Through a Prism

If a beam of white light is passed through a prism, a spectrum of different colours can be seen to emerge, including Red, Orange, Yellow, Green, Blue, Indigo and Violet. This is the visible light spectrum as we see it; each of these colours has its own wavelength within the range of 400 – 700 nanometres.


The Effect of White Light Refracted Through a Prism

The prism refracts light, enabling white light to separate into its individual components. A similar effect can be seen in a rainbow: when it rains, water droplets in the air refract the rays of sunlight; the curvature of the Earth produces the bow effect we are so familiar with.


Colour and Colouring Agents

Light can be influenced by two important rules of nature, additive colour and subtractive colour. Additive colour is simply colour generated from a light source, for example directly from the sun or a light bulb. However, when light hits an object it is influenced by the properties or colouring agents of that object – the pigment in hair can be described as a colouring agent.


Atomic Structure

Ultimately, it is the atomic or molecular structure of an object that influences how much light is reflected and absorbed. A molecule is constructed of a number of atoms, which are constantly moving around in ‘intermolecular space’; a process called the Brownian movement.


These Brownian movements are similar to light. If the vibration frequency is similar or synchronised, the light wave is reflected. If the vibration frequency is not similar, the light wave is absorbed.


Total Reflection
Total Absorption

The Effect of Light on a Black or White Surface

This explains why the sun easily warms up black objects. Black surfaces absorb all light waves and this extra energy warms up the material, whereas white objects reflect the sunlight and therefore absorb less energy.