The lighthouses or port entrance lights usually come in pairs, like those of the port of Trouville-Deauville at the level of the Touques estuary in the Calvados department. The two piers that frame its channel are terminated by a red light for one and a green light for the other. The red light is used to signal larboard and the green one for starboard. Both located in height, they are equipped with a lamp, an optical system, and a lantern. By day, the lights serve as fixed and identifiable landmarks, hence their different aspects.