Red Light on a Dark Surface

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This is one of a set of 3 diagrams showing torches projecting red, green and blue light onto a neutral coloured surface.

A fourth diagram shows what happens when all three torches are turned on at the same time and their beams partially overlap one another.

Understanding the diagrams:

  • The diagrams illustrate how the RGB colour model works in practice.
  • Each torch emits light at the same intensity.
  • Each torch points towards a different area of the surface.
  • The light in each case is of a single wavelength so produces a spectral colour.
  • The selected wavelengths are: red = 660 nanometres (nm), green = 525 nm, blue = 460 nm.
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Description

Red Light on a Dark Surface

TRY SOME QUICK QUESTIONS AND ANSWERS TO GET STARTED
Do mixtures of RGB primary colours produce spectral colours?
No! The colours produced by mixing primary colours are not spectral colours. Spectral colours are produced by a single wavelength of light.
Name three colours of light that added together make white?
When wavelengths corresponding with red, green and blue are projected onto a neutral coloured surface they produce white.
How many primary colours in an RGB colour wheel?
There are three primary colours in an RGB colour wheel.
Name three colours and their corresponding wavelengths of light that when see together make white?
When red (660 nm), green (525 nm) and blue (460 nm) colours of light are projected at the same intensity onto a neutral coloured surface they produce white.

About the diagram

About the diagram
  • This is one of a set of 3 diagrams showing torches projecting red, green and blue light onto a neutral coloured surface.
  • A fourth diagram shows what happens when all three are on at the same time and their beams partially overlap one another.
Understanding the diagrams
  • The diagrams illustrate how the RGB colour model works in practice.
  • Each torch emits light at the same intensity.
  • Each torch points towards a different area of the surface.
  • The light in each case is of a single wavelength so produces a spectral colour.
  • The selected wavelengths are: red = 660 nanometres (nm), green = 525 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 a full gamut of colours.
  • Red, green and blue are called additive primary colours in an RGB colour model because they can be added together to produce all other colours.
  • Each of the three beams 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 any two fully saturated additive primaries are combined they produce a secondary colour: yellow, cyan and magenta.
  • When fully saturated red, green and blue primary colours are combined they produce white.
  • Some RGB colour models can produce over 16 million colours by varying the proportion and intensity of each of the three component primary colours.
  • The additive RGB colour model cannot be used for mixing different colours of pigments, paints, inks, dyes or powder. To understand these colourants find out about subtractive colour.

Some key terms

RGB colour model
  • To be clear about the RGB colour model it is useful to remember first that:
    • The visible spectrum is the range of wavelengths of the electromagnetic spectrum that correspond with all the different colours we see in the world.
    • A spectral colour is a colour corresponding with a single wavelength of visible light, or with a narrow band of adjacent wavelengths.
    • The human eye, and so human perception, is tuned to the visible spectrum and so to spectral colours between red and violet. However, because of the way the eye works, we can see many other colours which are produced by mixing colours from different areas of the spectrum. A particularly useful range of colours is produced by mixing red, green and blue light.
    • RGB colour is an entirely different approach to producing and managing colour.
  • RGB colour is an additive colour model in which red, green and blue light is combined in various proportions to reproduce a wide range of other colours. The name of the model comes from the initials of the three additive primary colours, red, green, and blue.
  • Except for the three primary colours, RGB colours are not spectral colours because they are produced by combining colours from different areas of the visible spectrum.
  • RGB colour provides the basis for a wide range of technologies used to reproduce digital colour.
  • RGB colour provides the basis for reproducing colour in ways that are well aligned with human perception.
  • When an observer has separate controls allowing them to adjust the intensity of overlapping red, green and blue coloured lights they are able to create a match for a very extensive range of colours.
  • When looking at any modern display device such as a computer screen, mobile phone or projector we are looking at RGB colour.
  • Magenta is an RGB colour for which there is no equivalent spectral colour.
Wavelength

Wavelength is a measurement from any point on the path of a wave to the same point on its next oscillation. The measurement is made parallel to the centre-line of the wave.

  • The wavelength of an electromagnetic wave is measured in metres.
  • Each type of electromagnetic radiation, such as radio waves, visible light and gamma waves,  forms a band of wavelengths on the electromagnetic spectrum.
  • The visible part of the electromagnetic spectrum is composed of the range of wavelengths that correspond with all the different colours we see in the world.
  • Human beings don’t see wavelengths of visible light, but they do see the spectral colours that correspond with each wavelength and the other colours produced when different wavelengths are combined.
  • The wavelength of visible light is measured in nanometres. There are 1,000,000,000 nanometres to a metre.
ROYGBV

ROYGBV is an acronym for the sequence of hues (colours) commonly described as making up a rainbow: red, orange, yellow, green, blue, and violet.

What is the trichromatic colour model?

The trichromatic colour model is a theory of colour that establishes terms, rules and methods to enable human colour vision to be dealt with in both systematic and practical ways.

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