# 17-31-018

meteorological optical range

v

length of the path in the atmosphere that is required to attenuate by 95 % the luminous flux in a collimated beam from a source at a colour temperature of 2 700 K

Note 1 to entry: The value of the attenuation has been chosen so that the meteorological optical range provides an approximate measure of the commonly used concept of meteorological visibility.

Note 2 to entry: The meteorological optical range, v, is related to the atmospheric transmissivity, T, assumed to be uniform, by the formula
or
where d0 is the length specified in the definition of atmospheric transmissivity.
These formulae are sometimes written
or
with d0 set to unity.

Note 3 to entry: This entry was numbered 845-11-20 in IEC 60050-845:1987.

Note 4 to entry: This entry was numbered 17-772 in CIE S 017:2011.

Publication date: 2020-12