Irradiance and IlluminancePublished on 24/2/2012 and last updated on Wednesday 27th of June 2018 at 07:37:02 PM
Now the flux received by the surface And the flux received by the surface Where, Ie,λ radiant intensity and ω solid angle.
Again the radiant flux received per unit area for A1 and A2 are Here A1 and A2 are equal. Putting the φe,λ = Ie,λ ω in the equation we get This is Inverse Square Law of irradiance.
If we convert this irradiance into Illuminance then we should follow the conversion equation i.e. Where, Km is the constant which is called maximum spectral luminous efficacy and its value is 683 lm/W. By definition the luminous flux received by unit area of the detector is called Illuminance. Its unit is Lux or Lumen per sq. meter (lm/sq. m). It also follows the same inverse square law, i.e. Ev is related to the surface dA where luminous flux is falling on this surface perpendicularly. E'v is related to the surface dA' where this surface creates an angle Ɵ to the base plane. As per figure above, This above equation can be written making it generalized,