Lighthouse In Waves

To be effective the lamp must be high enough to be seen before the danger is reached by a mariner. The minimum height is calculated according to trigonometry by taking the square root of the height of a lighthouse in feet and multiplying it by 1.17 to yield the distance to the horizon in nautical miles.
Where dangerous shoals are located far off a flat sandy beach, the prototypical tall masonry coastal lighthouse is constructed to assist the navigator making a landfall after an ocean crossing. Often these are cylindrical to reduce the effect of wind on a tall structure, such as Cape May Light. Smaller versions of this design are often used as harbor lights to mark the entrance into a harbor, such as New London Harbor Light.
Where a tall cliff exists, a smaller structure may be placed on top such as at Horton Point Light. Sometimes, such a location can be too high – as along the west coast of the United States. In these cases, lighthouses are placed below clifftop to ensure that they can still be seen at the surface during periods of fog, as at Point Reyes Lighthouse. Another victim of fog was Point Loma Light (old) which was replaced with a lower lighthouse, Point Loma Light (new).
As technology advanced, prefabricated skeletal iron or steel structures tended to be used for lighthouses constructed in the 20th century. These often have a narrow cylindrical core surrounded by an open lattice work bracing, such as Finns Point Range Light.