Illuminance

The term Illuminance refers to the quantity of light that falls on a physical surface. Illuminance is typically used to define the usable light supplied by a natural or artificial light source regardless of its total luminosity.

  • If we place a book on a table, then different levels of illuminance can be observed when the sky is overcast, under the mid-day sun, in moonlight or artificial light.
  • Illuminance is independent of the surface that light falls upon. It is a description of the qualities of the light itself.
  • Illuminance is something that can be measured and so is an objective term.
  • The implication of this is that a 10-watt light-bulb is a fairly powerful source of light if it is placed next to an observer reading a book. But even a 1000-watt light-bulb will not provide enough light to read by if it is located a hundred metres away.