How do fixed directional lights use red and green sectors to guide ships?

In the context of coastal navigation, fixed directional lights are used to provide mariners with accurate guidance when approaching ports, harbors, and estuaries. These structures emit light in sharply defined red and green sectors to delineate safe passage or specific navigational channels.1

By observing which color sector they are currently in, navigators can determine their position relative to a safe course or hazard. These lights are distinct from rhythmic flashing lights, as they remain steadily burning to provide constant directional information. This method serves as a reliable visual aid, allowing vessels to maintain a safe heading through complex or narrow coastal waters without relying solely on electronic systems.12