Luminosity

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.
  • So luminosity refers to the total amount of light emitted by a source per unit time and is often measured in units like watts or lumens. It indicates the raw power of the light source, regardless of its colour or direction.
  • 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.
ABOUT LUMINOSITY & TRICHROMATIC COLOUR VISION
  • If you have read about trichromatic colour vision, you will know that it is possible to match any colour within the visible spectrum by appropriately mixing wavelengths of light corresponding with the three RGB primary colours (red, green and blue). This can be achieved without any loss of colour 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 mixture as 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 a 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).
ABOUT LUMINOSITY & LUMINANCE
  • Luminosity signifies the total amount of visible light emitted by a source, measured in watts or lumens. It’s like the raw power output of light, similar to an engine’s horsepower.
  • Luminance, on the other hand, tells us about the perceived brightness of that light when it reaches our eyes. It considers multiple factors:
    • Luminosity of the source
    • Reflection of the surface receiving the light
    • Human eye’s sensitivity to different wavelengths
  • Think of it this way: a powerful light source (high luminosity) might shine on a dark surface (low reflection), resulting in a lower perceived brightness (lower luminance).
  • Conversely, a weaker light source shining on a highly reflective surface could still lead to a higher perceived brightness due to the reflection boosting the received light.
Related diagrams

Each diagram below can be viewed on its own page with a full explanation.

References
  • 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.
  • So luminosity refers to the total amount of light emitted by a source per unit time and is often measured in units like watts or lumens. It indicates the raw power of the light source, regardless of its colour or direction.
  • 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.