Maritime beaconing and signaling include several categories of light, visual, sound, or radioelectric devices. Among them, the lights and lighthouses can be distinguished according to a certain number of criteria. Lighthouses must meet at least two of the following four: be more than 65 ft (20 m) high, provide light for more than 20 miles (32 km), house a commission office, and serve as a marking or large landfall, i.e mark the turns in shipping routes or the approach to a coast. Lights, on the other hand, must meet only one of these criteria.