Dispersion (or chromatic dispersion) refers to the way that light, under certain conditions, separates into its component wavelengths and the colours corresponding with each wavelength become visible to a human observer.

  • Dispersion is the result of the relationship between refractive index and wavelength.
  • Every wavelength of light is affected to a different degree by the refractive index of a medium and as a result, changes direction by a different amount eg. when passing from one medium (such as air) to another (such as glass). In the case of white light, the separate wavelengths fan out with red on one side and violet on the other.
  • A familiar example of dispersion is when white light strikes raindrops and a rainbow of colours become visible to an observer.
  • As light first enters and then exits a droplet it separates into its component wavelengths which the observer perceives as colour.
  • Colour is not a property of electromagnetic radiation, but a feature of visual perception.