IEVref:845-25-104ID:
Language:enStatus: Standard
Term: photometric distance law
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Definition: law relating the illuminance, E, on a real or imaginary surface to the luminous intensity, I, of an illuminating point source whereby

E= Icosθ d 2 MathType@MTEF@5@5@+= feaagKart1ev2aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbbjxAHX garuavP1wzZbItLDhis9wBH5garmWu51MyVXgaruWqVvNCPvMCG4uz 3bqee0evGueE0jxyaibaieYdi9WrpeeC0lXdh9vqqj=hEeea0xXdbb a9frFj0=OqFfea0dXdd9vqaq=JfrVkFHe9pgea0dXdar=Jb9hs0dXd bPYxe9vr0=vr0=vqpWqaaeaaciWacmGadaGadeaaeaGaauaaaOqaai aadweacqGH9aqpdaWcaaqaaiaadMeaciGGJbGaai4BaiaacohacqaH 4oqCaeaacaWGKbWaaWbaaSqabeaacaaIYaaaaaaaaaa@4023@

where θ is the angle between the normal to the surface and the line between the surface and the source and d is the distance between the source and the surface

Note 1 to entry: The photometric distance law strictly only applies for a point source. However, it can also be applied for non-point sources at sufficiently large distances within acceptable limits of error or measurement uncertainty; in this case the degree of approximation at the distance used should be confirmed by measurement.

Note 2 to entry: For radiometric sources the equivalent term is "radiometric distance law".


Publication date:2020-12
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