The Light List indicates that a light has a nominal range of 8 miles and is 48 feet(14.6 meters) high. If the visibility is 6 miles and your height of eye is 35 feet(10.7 meters), at what approximate distance will you sight the light?
• Nominal range vs. geographic range of a light • How to compute geographic range using height of eye and height of light • Effect of meteorological visibility on how far a light can actually be seen
• First, think about what the nominal range of a light represents and what it assumes about visibility conditions. • Next, consider how to find the maximum distance the light and your eye can see each other over the curvature of the Earth using their heights. • Then, decide which is limiting: the visibility conditions, the nominal range, or the distance to the horizon from both heights combined.
• Check whether the nominal range (8 nm) can actually be achieved when visibility is only 6 nm. • Calculate or estimate the geographic range using both heights (light and observer) and compare it with the other limits. • Make sure your final answer does not exceed the most restrictive of: nominal range, meteorological visibility, and geographic range.
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