a lighthouse is a tall building that sends out light for use in navigation. lighthouses are built on the coast of an ocean or lake. the lighthouse protects ships from crashing into shore, by sending the light out towards the sea. when sailors see the light, they know to avoid hitting the shore. the light usually turns in a circle so that ships see a flashing light. the light is usually covered by a fresnel lens. this lens enables the light to travel a far distance.