Definition
Nominal range is the luminous range of a light in a homogeneous atmosphere of meteorological visibility 10 nautical miles, and is the figure printed on British Admiralty charts, for example 18M. It depends only on intensity, not on height or on the observer's eye. In visibility better than 10 miles the actual luminous range is greater; in haze or rain it can be far less, and the luminous range diagram in the light list converts between them.
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