Running lights (or navigation lights) are essential safety lights displayed on a vessel from sunset to sunrise and in low-visibility conditions. They identify a boat's position, direction of travel, and type. Required by international law (COLREGs), they include red/green sidelights and white stern/masthead lights, helping sailors determine the "give-way" vessel and avoid collisions.

Key Components of Running Lights:
Sidelights (Port/Starboard): A red light on the left (port) and a green light on the right (starboard) are visible from straight ahead to 22.5 degrees aft of the beam.

Sternlight: A white light placed at the stern (rear), visible only from behind or near the rear of the vessel.

Masthead Light: A white light that shines forward and to both sides (225 degrees total). Required for power-driven vessels and must be positioned above the sidelights.

All-Round Light: A single white light visible 360 degrees, often used by smaller boats (23 ft) instead of separate masthead and sternlights.

Key Distinctions for Sailing Vessels:
Sailboats Under Sail: Display only sidelights and a sternlight.

Sailboats Under Power: Considered a power-driven vessel and must display a masthead light in addition to sidelights and a sternlight.

Visibility Regulations: The range and arc of visibility are strictly mandated based on the vessel's size.