Introduction

Short-range aids to navigation include lighted and unlighted beacons, ranges, leading lights, buoys, and their associated sound signals. Each short-range aid to navigation, commonly referred to as a "navaid", fits within a system designed to warn the navigator of dangers and direct him toward safe water. In this system, color, shape, light and sound characteristic, determine the function of the beacon. Beacons are stationary, visual navigation aids, also called "marks". Large lighthouses and small single-pile structures are both beacons, but with different functions. The specific function of a beacon can be read from the nautical chart or from other nautical publications.

Lighted beacons are called lights. Unlighted beacons are day beacons. All beacons may exhibit a day mark of some sort. In the case of a lighthouse, the color and type of structure are the day marks. In the case of buoys and day beacons well-defined geometrical shapes are used. The day mark should allow the identification of the function of the beacon when the color code cannot be determined, due to conditions of reduced visibility - e.g. during dusk or twilight.

During the time between sunset and sunrise, lights show distinctive light phase characteristics by which they can be identified. Knowing their location from the chart, lights are a great support to the navigator during the night time, as reference and bearing points.

Lights and lager day beacons are described e.g. in the "Admiralty List of Lights and Fog Signals" published by the United Kingdom Hydrographic Office (UKHO) or in the "List of Lights" published by the National Imagery and Mapping Agency (NIMA) and the US Coast Guard (USCG).