Spectral colour model

The spectral colour model is based on the specific wavelengths of light within the visible spectrum that the human eye is sensitive to, establishing a direct connection between each wavelength and a corresponding colour ranging from red to violet.

  • A spectral colour is a hue evoked in normal (trichromatic) human vision by a single wavelength of visible light.
  • The human eye is tuned to the visible spectrum and each wavelength of light corresponds with the perception of a spectral colour between red and violet.
  • A spectral colour is a monochromatic colour – monochromatic means containing one colour.
  • Every wavelength of visible light produces the experience of a monochromatic spectral colour with a hue different from any other.
  • All light sources including sunlight, artificial light, lightening, candles and glow worms emit a mixture of wavelengths of light and each wavelength corresponds with a spectral colour.
  • The colours we see in the world around us result from different combinations of wavelengths of light reflecting off the surfaces, media and objects before striking light-sensitive cells in our eyes.
  • Whilst the Sun emits wavelengths of light corresponding with all the colours of the visible spectrum an LED bulb may emit a single wavelength of light.
  • Although we can’t distinguish between them all, we see the full range of spectral colours when we see a rainbow or the spread of colours dispersed by a prism.
  • In everyday experience, a spectral colour is usually composed of a narrow band of adjacent wavelengths.
  • Spectral colours are sometimes called pure hues or monochromatic hues.
  • As sunlight travels through the air it is invisible but if it strikes a neutral-coloured surface and all wavelengths are reflected equally, it appears white.
  • Spectral colours are often shown as a strip of colours with red at one end and violet at the other.
  • The spectral colour model helps us to understand the connection between the physics of light and the perception of colour but other models are needed to help to make sense of how the eye works and to manage colour in different practical situations:
Non-spectral colour
  • A non-spectral colour is any hue that cannot be produced by light of a single wavelength (e.g. magenta).
  • Additive colour models such as RGB and HSB involve mixing red, green and blue light so do not produce spectral colours.
  • Spectral colours such as orange, yellow and violet can be mimicked by the RGB colour model. This involves mixing the RGB primaries, red, green and blue.
    • Red at 100% and green at 50% brightness produce orange
    • Red (100%) and green (100%) produce yellow
    • Red (50%) and blue (100%) produce violet.
Rainbow colours
  • Rainbow colours include red, orange, yellow, green, blue and violet but the human eye can distinguish many other spectral colours between each of these.
  • In a continuous spectrum of wavelengths, each separate hue is indistinguishable to the human eye.
  • The fact that we see the distinct bands of colour in a rainbow is often described as an artefact of human colour vision.
  • Spectral colours can be mimicked by RGB colour. This involves mixing coloured lights tuned to the three spectral primaries, red, green and blue.