Lighthouse

For effectiveness, the lamp must be high enough to be seen before the danger is reached by a mariner. The minimum height is calculated by trigonometry (see Distance to the horizon) as <math alt="D is 1.22 times the square root of H"> D = 1.22 \sqrt {H} </math>, where H is the height above water in feet, and D is the distance from the lighthouse to the horizon in nautical miles, the lighthouse range. 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.…