$C_d=C_0{T}^{d/d_0}$

where d₀ is the length specified for the definition of T

Note 1 to entry: The formula is sometimes written

$C_d=C_0{T}^{\delta }$

where the exponent, δ, in T^δ 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

$C_d=C_0({\mathrm{0,05}}^{d/v})$

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.