# 17-31-020

Koschmieder's law

law relating the apparent contrast, Cd, of an object against a sky background, at a given distance of observation, d, to the inherent contrast, C0, and to the atmospheric transmissivity, T, which is assumed to be uniform

where d0 is the length specified for the definition of T

Note 1 to entry: The formula is sometimes written

where the exponent, δ, in Tδ is the numerical value of d measured with d0 as "unit".

Note 2 to entry: Taking into account the relationship between atmospheric transmissivity, T, and meteorological optical range, v, given in Note 2 to entry of "meteorological optical range", Koschmieder's law can be also written as
.

Note 3 to entry: The contrast is taken to be the quotient of the difference between the luminance of the object and the luminance of the background, and the luminance of the background.

Note 4 to entry: This entry was numbered 845-11-22 in IEC 60050-845:1987.

Note 5 to entry: This entry was numbered 17-629 in CIE S 017:2011.

Publication date: 2020-12