Chart Navigation & Plotting · Aids to Navigation — Luminous vs Geographic Range
The range actually printed for a light on a U.S. chart is the nominal range. A light may still not be visible at that range if:
- AIt is below the horizon for your height of eye (geographic range is less) or visibility is below the standard 10 NM meteorological assumption✓ Correct
- BThe vessel's speed is too high
- CThe light is white rather than red
- DIt is daytime only
Explanation
Nominal range is the luminous range in standard visibility (meteorological visibility of 10 NM). The light is actually seen only if it is also above the horizon for the observer (geographic range) and if the prevailing visibility meets or exceeds the standard. Compute the lesser of luminous and geographic range and adjust for actual visibility.
Authority: Bowditch (Pub. No. 9); Light List
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