Lighthouses are used in shipping the ships to show the way in important or dangerous places. They provide a navigation aid dar. One finds lighthouses in harbor entrances and near the coast.
Important for a lighthouse is that it is visible from afar. Due to the curvature of the earth, a lighthouse must have a certain height so that it can be seen from afar. Visibility alone is not enough, especially in misty, foggy weather, the luminosity and the light color are responsible for the visibility.
The first beacons at the beginning of the seafaring were simple torches. Later it became open fire, later gas lights were used for lighting. To improve visibility, lenses or mirrors were used to focus the light. Today beacons are operated electrically.
A distinction is made between seafires (these serve ships as an announcement of the approaching mainland), orientation fires (these are used for orientation and positioning near the coast) and fire for marking narrow fairways.
Beacons have an identifier, by the sequence of light and pauses in between each beacon becomes identifiable if it is contained in a beacon directory. The beacon of the island Norderney sends as identifier eg 15 flashes per minute.