The Luminous Range Diagram shown in the Light List is used to convert the nominal range to the luminous range. When using this diagram, it must be remembered that the ranges obtained are approximate, the atmosphere may vary between the observer and the light, and glare from background lighting will reduce considerably the range at which lights are sighted. The Luminous Range Diagram is entered with the nominal range at the bottom" nominal range scale" a vertical line is followed up until it intersects the visibility curve or reaches the region on the diagram representing the meteorological visibility, from this point ( you take 90° turn to starboard.
Example 1 The nominal range of a light as extracted from the Light List is 15 nautical miles. Required - The luminous range when the meteorological visibility is:
(1) 11 nautical miles
(2) 1 nautical mile.
Solution - To find the luminous range when the meteorological visibility is 11 nautical miles, the Luminous Range Diagram is:
(1) entered with nominal range 15 nautical miles on the bottom nominal range scale.
(2) a vertical line is followed up until it meteorological visibility of 11 nautical miles
(3) from this point (you take a 90 degree turn to starboard) a horizontal line is followed until it intersects the luminous range scale at 16 miles
A similar procedure is followed to find the luminous range when the meteorological visibility is 1 nautical mile.
Answers - (1) 16 nautical miles, (2) 2.8 nautical miles.