Cones of colour

Rainbows can be modelled as a set of six nested cones with the apex of each aligned with the lenses of an observer’s eyes.

  • Each cone has a different radius and each is composed of a narrow spread of wavelengths of light that determines its apparent colour. Red fills the cone with the largest radius and violet fills the smallest.
  • The cones do not have a simple 2D base. At their nearest, droplets may be within reach of an observer. At the other extreme, distant raindrops also refract and reflect light back towards an observer.
  • Modelling a rainbow as a cone that shows depth, as well as height and width, demonstrates that all the raindrops contained within one of the cones at any moment can contribute to the visual experience of an observer regardless of how far they are away.
  • Whilst modelling rainbows as discs corresponds with what an observer sees, the idea that rainbows are formed from cones of colour corresponds with a diagram showing a side elevation with the Sun, observer and rainbow arranged along the rainbow’s axis.