"Robert M. Gary" wrote in message
...

I think part of the problem is that the FAA defines visibility during
the day as the ability to see an unlit object but we're looking at
high intensity lights in this case. You may only be able to see
something w/o lights 1/8mile away but may be able to see a strobe
light 1/2 mile away.


Prevailing visibility is defined as the greatest distance that can be seen
throughout at least half the horizon circle, not necessarily continuous.
The definition does not change at night. Dark or nearly dark objects viewed
against the horizon sky are to be used as visibility markers during the day,
and unfocused lights of moderate intensity (about 25 candela) are to be used
during the night. This applies only to human observers, of course.
AWOS/ASOS doesn't care if it's day or night.