Overlapping Beams of Blue and Red Light Make Magenta




To find out more about the diagram above . . . . read on!

Overlapping Beams of Blue and Red Light make Magenta

Look carefully at the diagram at the top of the page. Now check out the following questions (and answers)!

  1. In which colour model is magenta a primary colour?
  2. What are the two primary colours of light that together make magenta?
  3. Is magenta a spectral colour?
  4. In which colour model is magenta a secondary colour?
  5. What is the difference between the CMY colour model and the four-colour CMYK inks used by printers?

About the Diagram

Introducing the diagram! Read back and forward between the image at the top of the page and the explanation below!

This is one of a set of 3 diagrams showing pairs of RGB primary colours projected onto a neutral coloured surface.

In this diagram blue and red primary colours overlap to produce magenta.

Understanding the diagrams

  • The diagrams illustrate how the RGB colour model works in practice.
  • The two primary colours in each diagram are of the same intensity.
  • The light sources are arranged so that the colours overlap.
  • The light source in each case is produced by a single wavelength of light.
  • The selected wavelengths are: red = 660 nanometres (nm), blue = 460 nm.

About the RGB colour model

  • RGB colour is an additive colour model that combines wavelengths of light corresponding with the red, green and blue primary colours to produce other colours.
  • RGB colour is called a model because it is a method that can be followed to produce any colour from a combination of red, green and blue light sources.
  • Red, green and blue are called additive primary colours in an RGB colour model because they can be added together to produce other colours.
  • When mixing light, each RGB primary colour is called a component of the resulting colour.
  • Different colours are produced by varying the intensity of the component colours between fully off and fully on.
  • When the light sources that produce the red, green and blue primary colours are at full intensity, together they produce white.
  • Each light source at full intensity produces a fully saturated colour.
  • When any two fully saturated RGB primaries are combined they produce a secondary colour (yellow, cyan or magenta).
  • Some applications of the RGB colour model can produce over 16 million colours by varying the intensity of each of the three component primary colours.
  • The additive RGB colour model cannot be used for mixing opaque pigments, paints or powders. To understand these colourants find out about subtractive colour models.
  •  The RGB colour model does not define the precise wavelength (or band of wavelengths) for the three primary colours.
  • When the exact composition of primary colours are defined, the colour model then becomes an absolute colour space.

Follow the blue links for definitions . . . . or check the summaries of key terms below!

Some Key Terms

Move to the next level! Check out the following terms.

Colour wheel

A colour wheel is a diagram based on a circle divided into segments. The minimum number of segments is three ...
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Primary colour

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

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

A colour model is a mathematical system used to describe colours using a set of numeric values. A colour model ...
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White light

White light is the name given to visible light that contains all wavelengths of the visible spectrum at equal intensities ...
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