Rainbows and rays of light

A ray of light (light ray or just ray) is a common term when talking about how and why rainbows appear.

  • The idea that light is made up of rays is so commonplace when describing and explaining rainbows that it is easily taken for granted.
  • The idea of light rays is useful when trying to model how light and raindrops produce the rainbow effects seen by an observer.
  • Light rays don’t exist in the sense that the term accurately describes a physical property of light. More accurate descriptions use terms like photons or waves.
  • Modelling light as rays is a way to discuss and represent the path of light through different media in a simple and easily understandable way.
  • When light rays are drawn in a ray-tracing diagram they are represented as straight lines connected at angles to illustrate how light moves and what happens when it encounters different situations and conditions.
  • More accurate descriptions of light use terms such as photons or electromagnetic waves.
  • Don’t forget that:
    • The incident rays of light that contribute to a rainbow seen by an observer are those that approach raindrops parallel with the rainbow axis.
    • To understand why incident rays are always parallel with the rainbow axis we need to think in terms of what the observer sees. See: 2.7 Observer’s point of view.