Spectral Colours & RGB Colours



Spectral Colours & RGB Colours

Yes! When spectral colours are arranged in a diagram, the order in which they appear corresponds with their wavelength. The easiest way to show this is a band of colours of increasing wavelength with red at one end and violet at the other.
Spectral colours are all the colours between red and violet that can be produced by a single wavelength of light. Sunlight is composed of spectral colours.
A non-spectral colour is any colour that is not be produced by a single wavelength of visible light.
_x000D_ _x000D_ Red, green and blue are the three primary colours in the RGB colour model.

About the diagram

About the diagram
  • This diagram shows the six spectral colours associated with the colours of the rainbow.
  • The top half of the diagram shows that each of these spectral colours can be produced by a single wavelength of light.
  • The bottom half of the diagram shows that three spectral colours (red, green and blue) can be combined in pairs to produce orange, yellow and violet.
Remember that:
  • Spectral colours are produced by a single wavelength of light. So each individual wavelength of visible light produces a different spectral colour.
  • Rainbows are produced by spectral colours as sunlight is refracted and dispersed by raindrops.
  • Red, orange, yellow, green, blue and violet are familiar spectral colours.
  • The visible spectrum contains a continuum of spectral colours.
  • The wavelength corresponding with each colour is shown in nanometres (nm). The wavelengths selected for each colour are for illustration only.
  • In practice, the choice of wavelengths for primary colours usually depends on factors such as the colour model being used, the gamut of colours that a display device can produce and the context in which colours are to be viewed.
Remember also:
  • The visible spectrum is a small part of the electromagnetic spectrum.
  • Spectral colours should not be confused with RGB colours.
  • Spectral colours relate to the visible spectrum.
  • RGB colours are produced by mixing wavelengths using the three primary colours, red, green and blue.
  • A demonstration of RGB colour is often presented in the form of a colour wheel.
  • In a continuous spectrum of wavelengths, separate colours are indistinguishable to the human eye.
  • The fact that we see distinct bands of colour in a rainbow is an artefact of human colour vision.

Some key terms

Visible spectrum

The visible part of the electromagnetic spectrum is called the visible spectrum. The visible spectrum is the range of wavelengths ...

RGB colour

To be clear about RGB colour it is useful to remember first that: The visible spectrum is the range of ...

Primary colour

Primary colours are a set of colours from which others can be produced by mixing (pigments, dyes etc.) or overlapping ...


Wavelength is a measurement from any point on the path of a wave to the same point on its next ...

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