What is Colour?

To understand what colour is, it is necessary to first look at the source of colour.

The source of colour is light where pure white light, such as the sun’s rays, contains all the colours of the visible spectrum.

The visible spectrum of colours is all the colours we can see between red and violet as in a rainbow: red, orange, yellow, green, blue, indigo and violet.


So if the source of colour is light, what is light?

Light is waves of energy travelling through space. It is the only energy we can see and we see it in the form of white light and colours.

To understand what waves of energy are, consider the waves in a pool. If you jump into the water, waves will travel from the point of impact to the other side of the pool. The waves created are a result of the energy from your splash and that energy moves across the pool.

Note that it is only the energy moving and not the water.

Therefore, a wave is energy moving in a particular direction.

What are waves of energy?

Waves of energy are positive and negative charges that are constantly vibrating and producing electromagnetic waves travelling at incredibly high speeds all over the Universe. Together they form part of the electromagnetic spectrum.

What is the Electromagnetic Spectrum?

Visible light is actually a very small part of the electromagnetic spectrum.

Visible light energy is made up of many frequencies and wavelengths and falls between Infrared and Ultraviolet.

The rest of the Electromagnetic spectrum is made up of many other waves and energy including radio waves, microwaves, infrared waves, ultraviolet waves, X-Rays and gamma rays which are invisible to the human eye.

Electromagnetic radiation itself can be described as being a stream of photons (massless particles) moving at the speed of light (186,000 miles per second) and travelling in a wave-like pattern. All electromagnetic radiation, consists of these photons each having its own energy.

Different forms of electromagnetic radiation have different amounts of energy. Radio waves, for example, have less energy than microwaves. The reason for this is because the photons of radio waves have a lower frequency or cycles per second – hertz ( Hz for short) and therefore less energy.


How are light waves measured?

Light and colours are measured in wavelengths (nanometers), where each colour has its own wavelength and frequency. The size of each wave is calculated by determining the distance between corresponding points on consecutive waves. This is normally done by measuring from peak to peak or from trough to trough.


When it comes to light, you can only see wavelengths of 380-780 billionths of a meter (actually referred to as nanometers where 1 billionth of a meter = 1 nanometer).

Wavelengths can be as small as one billionth of a meter (1 nanometer), like in gamma rays. They can also be as long as centimetres or meters, like in radio waves.

Frequency is the number of waves that pass a point in space during any time interval, usually one second. We measure it in units of cycles (waves) per second, or hertz.

The frequency of visible light is referred to as colour and ranges from 430 trillion hertz, seen as red, to 750 trillion hertz, seen as violet.

The higher the frequency, the shorter the wavelength.

Therefore violet has the highest frequency and the shortest wavelength and red has the lowest frequency and the longest wavelength of the visible spectrum.

How do we perceive colour?

The colours we perceive in our world are the result of light striking the surfaces of objects around us whereupon, and depending on the quality of the surface and its properties, some colours of the spectrum contained in the light are absorbed and some are reflected back at our eyes.

What is reflected back at our eyes is transmitted via cones and rods to our brains, which in turn translate these messages into the particular colours that we perceive.

colour reflection

It is important to note that the ambient lighting conditions prevalent at the time will further influence the quality (value, tone and intensity) of the colours that we perceive (light or dark, sunrise or sunset, natural light or artificial light, light reflected from nearby surfaces).

More about the physics behind how we see colours in my next post.



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