A lighthouse is a tall, tower- like building with a powerful signaling lantern at the top. The beam of light from the lantern sweeps across the sky at regular intervals in all directions, guiding ships at sea. The beam is concentrated, and focused by special lenses, so that it can travel a very long distance.
The first lighthouse optics, that was designed by the french inventor Augustin Jean Fresnel, combined highly polished prisms with an array of lenses that captured light and funneled it back into a main beam. This light could be seen for more than 32 kilometers.
many of today's lighthouse have a system of rotating lenses, and the newer ones flash off and on as way of conserving energy.