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Intensity measures the energy carried by a light wave or stream of photons:

  • When light is modelled as a wave, intensity is directly related to amplitude.
  • When light is modelled as a particle, intensity is directly related to the quantity of photons present at any given point in time.
  • The intensity of light falls exponentially as the distance from a point light source increases.
  • Light intensity at any given distance from a light source is directly related to its power per unit area, where the area is measured on a plane perpendicular to the direction of propagation (travel) of the light.
  • The power of a light source describes the rate at which light energy is emitted and is measured in watts.
  • The intensity of light is measured in watts per square meter (W/m2).