Luminosity refers to the total amount of light being given off by a source, regardless of the direction.

  • The luminosity of a light source depends on the total amount of power it consumes and the efficiency with which it converts that power into visible light.
  • Luminosity is a measurable quantity and is often used as an objective measure of the total amount of light being emitted by a source.
  • The maximum luminosity of a display device corresponds with the brightest white it can reproduce and is called the white point.
  • The black point corresponds with the minimum luminosity of a device, so corresponds with the device being turned off.
  • The contrast ratio of the maximum and minimum luminosity of a television or computer screen is typically more than 280:1
  • If you have read about trichromatic colour vision, you will know that it is possible to match all the colours in the visible spectrum seen by an observer by appropriate mixing of wavelengths and intensities (luminosity) of light corresponding with three primary colours and this can be achieved without any loss of information so far as an observer is concerned.
  • Now imagine three light sources with wavelengths corresponding with red, green and blue connected to sliders that allow the luminosity of each component to be adjusted between a minimum of 0% (off) and a maximum of 100% (fully on).
  • When all three components have the same maximum luminosity, the observer perceives the additive primary colour of white.
  • If the sliders that control each light are set to the same value (and so to the same luminosity) between 1% and 99% then the result is a shade of grey, which appears darker as the intensity decreases or brighter as the intensity increases.
  • When the luminosity of each slider is set to different values, the result is the perception of colour.
  • When one of the components has the highest luminosity, the colour will be a hue near that primary colour and so appear more reddish, greenish or bluish. When two components have the same high luminosity, then the observer sees the hue of a secondary colour (a shade of cyan, magenta or yellow).