White light

White light is the name given to visible light that contains all wavelengths of the visible spectrum at equal intensities.

  • The sun emits white light because sunlight contains equal amounts of all of the wavelengths of the visible spectrum.
  • As light travels through a vacuum or a medium it is described as white light if it contains all the wavelengths of visible light.
  • As light travels through a vacuum or the air it is invisible to our eyes.
  • The term white light has two meanings. It can refer to:
    •  A mixture of all the wavelengths of visible light travelling through space without reference to its observation.
    • What an observer sees when all the colours that make up the visible spectrum strike a white or neutral-coloured surface.
  • The human eye also sees white when the wavelengths of light corresponding with the three primary colours red, green and blue (RGB) are projected onto a neutrally coloured surface.
  • White light appears coloured when some wavelengths of light are reflected by the surface of an object but others are absorbed.
  • Artificial light sources typically emit light with an uneven distribution of wavelengths or intensities and so do not emit white light.
  • Whilst there is no single, unique specification for white light, it is reasonable to argue that in any specific situation:

Why do light bulbs glow if light is invisible?

  • Incandescent light bulbs work by passing an electrical current through a fine tungsten filament that has a high electrical resistance.
  • The resistance causes electrons within the filament to heat up and to appear a very bright yellowish-white colour. This colour is produced by:
  • Independent of these observed properties, the filament also emits a full range of wavelengths of light that propagate without encountering obstacles and so remain entirely invisible to an observer.
  • The light emitted by a tungsten bulb spans wavelengths between 200 and 3000 nanometers.

White light is the name given to visible light that contains all wavelengths of the visible spectrum at equal intensities.

  • As light travels through a vacuum or a medium it is described as white light if it contains all the wavelengths of visible light.
  • As light travels through the air it is invisible to our eyes.
  • When we look around we see through the air because it is very transparent and light passes through it.
  • The term white light doesn’t mean light is white as it travels through the air.
  • One situation in which light becomes visible is when it reflects off the surface of an object.
  • When white light strikes a neutral coloured object and all wavelengths are reflected then it appears white to an observer.