In nautical navigation, lighthouses use lateral markers to help seagoing vessels find safe pathways through the water. Ships and boats interpret messages based on the marker's position, numbering, shape, coloring and lighting style. Lateral markers are designated by the International Association of Lighthouse Authorities.
Correct interpretation of lateral markers depends on a ship's orientation. For a vessel returning from the sea, the starboard, or right side, lateral interpretation is in effect. Therefore, the ship should keep any red lights to its right side and green lights to its left. For outgoing vessels, the port, or left side, interpretation holds that the green lighting should be on the left side. As a further navigational aid, the red lights are triangular and the green lights are rectangular.