There are no traffic lights in sea or sky, but the navigation light helps prevent collisions on the water or in the air. Ships, boats, and aircraft use navigation lights at night and during poor visibility to show their position and direction in order to avoid collisions. For most vessels under way with motor power, more than one navigation light is required. Different colors, locations, and patterns of navigation lights are mandated by international convention. International and national rules and regulations also govern the range, location, angle, and layout of navigation lights, depending on size, type, and activity of the craft.
Required to run from sunset to sunrise and during times of poor visibility, such as fog, a typical electric navigation light indicates to other mariners or fliers the size, speed, type, and direction of a watercraft or aircraft. For boats and ships, two sidelights are required. A red light is positioned on the port, or left, side near the bow, or front, while a green light is required on the starboard, or right side. These lights warn craft approaching from the front or sides of the vessel.
A white stern light is required on the stern, or back, of a boat or ship so that vessels approaching from the rear can see it. Larger boats and ships must also carry one or two masthead lights, depending on size of the craft. An all-around white light may be used on boats smaller than 39.4 feet (12 m) in place of masthead and stern lights. When they see a warning navigation light on another vessel, captains of a give-way vessel, as defined by international rules of the road, must take all measures, including changing course, slowing down, stopping, or even reversing course, to avoid a collision.
Certain nonmotorized boats are exempt from many of the requirements for navigation lights. Sailboats under 65.6 feet (20 m) and under sail power alone need only show a tricolored masthead light. Boats not powered by motors and under 23 feet (7 m), including canoes, kayaks, rowboats, and sailboats, need only carry a flashlight.
Special lighting rules apply for different situations. A boat at anchor, for instance, is required to exhibit a white anchor light, but all other lights, including sidelights, must be extinguished. Unique patterns and colors of lights differentiate high-speed ferries, dredgers, boats towing other boats, dive boats conducting night dives, and fishing boats dragging nets. These patterns alert other mariners to possible dangers such as nets, towlines, and unusual speeds and activities.
Aircraft and spacecraft are required to use lights in a similar manner as boats and ships. A red sidelight is mounted on the left wing, a green side light on the right wing, and a white light on the tail. Aircraft also use blinking strobe lights or a red or white rotating beacon light to help avoid collisions.
