The common name for the large, round structure at the top of a lighthouse is a lantern. This component contains the light source, which helps guide ships and boats safely to shore by providing a visible signal during both day and night. Lanterns are crucial in maritime navigation, as they can vary in color, intensity, and flashing patterns, allowing sailors to identify specific lighthouses from a distance. The design of lanterns has evolved over time, from simple oil lamps to modern electric lights, and they remain integral to coastal and oceanic safety, ensuring the safe passage of vessels in treacherous waters.