When discussing light,  a spectrum is a linear scale of spectral colours organised by wavelength.

  • A spectrum or spectra (plural) are produced naturally when light is refracted by a prism or by rain.
  • A diagram of spectral colours is usually presented in the form of a spectrum, a linear band organised by wavelength with red at one end and violet at the other.
  • Spectra are often shown in an elongated form so that as many different gradations of colour can be seen as possible.