Bands of colour, spectral and non-spectral colours

About bands of colour, spectral and non-spectral colours

Bands of colour

• Bands of colour are composed of a continuous range of wavelengths, so for example:
  • A continuous range of wavelengths between 750 – 620 nanometres (nm) typically appear red to an observer.
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  • Wavelengths between 590 – 570 nm will typically appear yellow.
  • A continuous range of wavelengths between 450 – 380 nm will typically appear violet.

Spectral colours

• A spectral colour is a colour that is evoked by a single wavelength of light (or narrow band of wavelengths) within the visible spectrum.
• Spectral colours are the colours red to violet.
• Diagrams of the spectral colour model are linear and may show colours selected:
  • Using equal and incremental steps in wavelength.
  • According to equal and incremental steps in the appearance of colours.

Non-spectral colours

• Non-spectral colours are produced by additive mixtures of wavelengths of light.
• Examples of non-spectral colours produced by two spectral colours are:
  • Purple – produced by mixing wavelengths corresponding with red and violet. Red (740nm) and violet (400nm) are at the extreme limits of the visible spectrum.
  • Magenta –  produced by mixing red (660nm) and blue (490nm).
  • Mauve – produced by mixing orange (600nm) and blue (450nm).
  • Examples of non-spectral colours produced by three spectral colours are:
    • Tints
    • Greys
    • Shades
    • So all achromatic colours are non-spectral colours.
• Whilst both spectral and non-spectral colours are produced by mixing a combination of colours corresponding with different wavelengths of light:
  • The RGB colour model produces a full gamut of colours by mixing red, green and blue primary colours in different proportions.
  • The CMY colour model produces a full gamut of colours by mixing cyan, magenta and yellow primary colours in different proportions.