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 the air it is invisible to our eyes.
  • White light is what an observer sees when all the colours that make up the visible spectrum strike a white or neutral coloured surface.
  • The 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.
  • Light is only visible as it is emitted by an object such as an electrical filament or when it strikes an object.
  • 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.
  • Whilst there is no single, unique specification of “white light”, there is indeed a unique specification of “white object”, or, more specifically, “white surface”.
  • A perfectly white surface diffusely reflects (scatters) all visible light that strikes it, without absorbing any, irrespective of the light’s wavelength or spectral distribution.
  • Since it does not absorb any of the incident light, white is the lightest possible colour. If the reflection is not diffuse but rather specular, this describes a mirror rather than a white surface.
  • Reflection of 100% of incident light at all wavelengths is a form of uniform reflectance, so white it is an achromatic colour, meaning a colour without hue.