photometric distance law
law relating the illuminance,
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".
Note 3 to entry: This entry was numbered 17-912 in CIE S 017:2011.