Nominal range luminous range

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The nominal range of a light is the maximum distance at which a light can be seen when the visibility is 10 nautical miles.
The light's nominal range can be found in the Yachtsmans Almanac
The luminous range of a light is the maximum range at which an observer can see a light under existing visibility conditions.
Luminous range does not take into consideration the elevation of the light, nor the observer's elevation.
The luminous range can be determined by knowing the nominal range of the light and the existing visibility.