What is visibility in weather?
According to the World Meteorological Organization (WMO) observation guidelines, atmospheric visibility is a physical quantity of atmospheric transparency (or turbidity), which described by distance from the point of view to the target object, which can be seen and identified.
Meteorological Visibility at Day refers to the maximum distance, that a suitable scale black object can be seen and identified , when observed against scattered light background such as fog.
Meteorological Visibility at Night refers to the maximum distance from which an appropriate scale of black object can be seen and recognized, or a object can be seen and recognized from medium intensity luminous.
Assuming that the overall illumination increases to the normal daytime level. The latter definition is more in line with the actual operation of night visibility measurement.