When an element or compound is heated it emits electromagnetic radiation of different wavelengths.

  • The Sun emits the full spectrum of electromagnetic radiation including all wavelengths of light from low energy radio waves to very high energy gamma rays.
  • Artificial light sources, including lamps of all kinds, typically emit more limited bands of wavelengths of visible light.
  • When looking directly at a light source, its colour corresponds with the wavelengths being transmitted.
  • Display devices such as computer screens emit wavelengths corresponding to red, green and blue primary colours. These are combined in different proportions to produce as many as 16 million colours.
  • Printing relies on the reflection of light off a white surface such as a sheet of paper. The surface is overlaid with inks. Transparent inks allow light to pass through to the paper where it is reflected back towards the observer. The colour of the light determines which wavelengths pass through the ink after reflection and so which colours an observer sees.
  • When light strikes opaque inks some wavelengths are absorbed and some are reflected off the surface.