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post #5 of Old 07-18-2011
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There three different light ranges:

A light’s luminous range is the maximum range at
which an observer can see a light under existing visibility
conditions. This luminous range ignores the elevation of the
light, the observer’s height of eye, the curvature of the
earth, and interference from background lighting. It is determined
from the known nominal range and the existing
visibility conditions. The nominal range is the maximum
distance at which a light can be seen in weather conditions
where visibility is 10 nautical miles.
A light’s geographic range depends upon the height of
both the light and the observer. Sum the observer’s distance to
the horizon based on his height of eye and the light’s distance
to the horizon based on its height to calculate a light’s geographic

Light lists usually provide the nominal range.

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