Nomenclature of the lights
This page is under construction
Lights exhibit a distinctive appearance by which they are recognized, e.g. Fixed, Flashing, Group Flashing, etc. The properties of their appearance, by which they are distinguished, are referred to as the characteristics of the light.
The principal characteristics are generally the sequence of intervals of light and darkness, and, in some cases, the sequence of colors of light exhibited.
Fixed lights—those which exhibit a continuous steady light.
Rhythmic lights—those which exhibit a sequence of intervals of light and eclipse (repeated at regular intervals) in a manner described in Chart No. 1 and this volume.
Alternating lights—rhythmic lights which exhibit different colors during each sequence.
Period of a light—the time occupied by an entire cycle of intervals of light(s) and eclipse(s).
Range: Meteorological visibility—the greatest distance at which a black object of suitable dimensions can be seen and recognized against the horizon sky or, in the case of night observations, could be seen and recognized if the general illumination were raised to the normal daylight level. Luminous range of a light—the greatest distance at which a light can be seen merely as a function of its luminous intensity, the meteorological visibility, and the sensitivity of the observer’s eyes.
Nominal range of the light—the luminous range of a light in a homogeneous atmosphere in which the meteorological visibility is 10 nautical miles.
Geographical range of a light—the greatest distance at which a light can be seen as a function of the curvature of the earth, the height of the light source and the height of the observer. The visibility of a light is usually the distance that it can be seen in clear weather and is expressed in nautical miles. Visibilities listed are values received from foreign sources.
Range lights—two or more lights at different elevations, so situated to form a range (leading line) when brought into transit. The light nearest the observer is the front light and the one farthest from the observer is the rear light. The front light is normally at a lower elevation than the rear light.
Directional lights—lights illuminating a sector of very narrow angle and intended to mark a direction to be followed. Vertical lights—Two or more lights disposed vertically or geometrically to form a triangle, square, or other figure. If the individual lights serve different purposes, those of lesser importance are called Auxiliary lights.
Occasional lights—lights exhibited only when specially needed:
(a) Tidal light—shown at the entrance of a harbor, to indicate tide and tidal current conditions within the harbor.
(b) Fishing light—for the use of fishermen and shown when required.
(c) Private light—maintained by a private authority for its own purposes. The mariner should exercise special caution when using a private light for general navigation.
Seasonal lights—usually shown only during the navigation season or for a lesser time period within that season.
Articulated lights—offshore aids to navigation consisting of a length of pipe attached directly to a sinker by means of a pivot or such other device employing the principle of the universal joint. The positional integrity is intermediary between that of a buoy and a fixed aid.
Aeronautical lights—lights of high intensity which may be the first lights observed at night from vessels approaching the coast. Those lights situated near the coast are listed in the List of Lights in order that the navigator may be able to obtain more information concerning their description.
These lights are not designed or maintained for marine navigation and they are subject to change without prompt notification. These lights are indicated in this List by the designation
AVIATION LIGHT and are placed in geographical sequence in the body of the text along with lights for surface navigation.
Aeromarine lights—marine-type lights for which part of
the beam is deflected to an angle of 10 to 15 degrees above
the horizon to facilitate use by aircraft.
Sector limits and arcs of visibility—these are arranged clockwise and are given from seaward toward the light. Thus, in the diagram, the sectors of the light are defined as: obscured from shore to 302°, red to 358°, green to 052°, white to shore. These are bearings of the light as seen from a vessel crossing the sector lines.
Under some conditions of the atmosphere, white lights may have a reddish hue. The mariner should not judge solely by color where there are sectors but should verify this position by taking a bearing of the light. On either side of the line of demarcation between white and red there is always a small sector of uncertain color, as the edges of a sector of visibility cannot be clearly defined.
When a light is obscured by adjoining land and the arc of visibility is given, the bearing on which the light disappears may vary with the distance from which it is observed. When the light is cut off by a sloping point of land or hill, the light may be seen over a wider arc by a ship farther off than by one closer.
Bearings—all bearings are true, measured clockwise from 000°, and given in degrees or degrees and minutes.