The Light List indicates that a light has a nominal range of 13 miles and is 36 feet high. If the visibility is 17 miles and your height of eye is 25 feet, at what approximate distance will you sight the light?
• Geographic range vs. luminous (nominal) range of a light • Use of height of eye and height of light with the distance-to-horizon formula • Choosing the shorter of the luminous/nominal range and the geographic range
• First, figure out how to find the geographic range between your eye and the light using their heights. What standard formula or table is used for that? • Compare the geographic range you find with the light’s nominal range of 13 miles and the meteorological visibility of 17 miles. Which one limits what you can actually see? • Look at the answer choices and decide which one best matches the limiting factor once you’ve calculated the geographic range.
• Compute the distance to the horizon for the light’s height and for your height of eye (both in feet), then add them for the geographic range. • Confirm that you are not simply using the 17 miles visibility or the 13 miles nominal range alone; you must compare them to the geographic range. • Ensure your final choice is not greater than both the geographic range and the nominal range, because you can’t see farther than either physical or luminous limits.
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