The term ‘light marking’ defines the device that is installed outside from the vessel and emits light from a determined geographical point in order to help the mariner to determine his position, to navigate with safety, to mark and warn for nautical dangers and other obstacles.
In general, these devices are called ‘lights’ and are either permanently installed in the ground, in the shores, in the sea floor or they float anchored.
Lights are divided into:
Lighthouses: Are the lights that are installed in specific positions so as to help the mariner to determine his position.
(Minor) Lights: Are the lights that are used in order to show something specific to the mariner (the entrance of a harbor, shallow waters, etc).
Light Buoys: Are the lights installed on a buoy that is anchored for the marking of a reef, a danger, etc.
Light Vessels: Are the lights that are installed on anchored vessels.
In the past, when the lights’ technology was in its infancy, the production and dispersion of the light required the human presence. Thereby, lights were manned with specialized personnel, the light keepers that were settled in the dwellings located in the light houses. These lights ware called ‘watched lights’. Globally, a great number of lights are still ‘watched’ until today. Later, because of the technology’s development in the area of navigational marking the majority of the lights started to function without the human presence. These lights are called ‘unwatched’. In fact, the unwatched lights are automatic, given that they start automatically when the sun’s light is concealed (during the twilight or during the day because of cloudiness) and they also turn off automatically when the sun’s light comes out. Nowadays, the majority of the lights that are installed or replaced function automatically. Thus, human presence is necessary only at the time of inspection and maintenance. In Greece all lights are automatic.
As noted before, lights (in this category lighting buoys are included) guide mariners with safety during the night. Consequently, the lighting signals of a neighboring area must be characterized by their special lighting appearance which makes possible their recognition between other lights of the specific area. Thereby, lighting signals emit in their own special succession, in periods of light and darkness or light with different coloring. This special distinctive mark with which every lighting signal is discerned from the others is called characteristic or character of the light. In other words, ‘characteristic of the light’ is called the visible and specific sight of the lighting phenomenon which the light produces and allows its secure recognition and distinction between the others.
Except from the general distinction of lighting markings in lights and minor lights according to the stableness and duration of the light they emit, lights are divided into three main categories:
- Fixed Lights (F). They emit a continuous and stable light, without discontinuities or alterations of its characteristics. Fixed lights are of various coloring (white, red, green, yellow).
- Rhythmic Lights (R). They emit light that presents discontinuities in a stable periodicity (flashing lights, occulting lights etc).
- Alternating Lights (Alt). They emit variations of colors (white, red, green) to a specific direction.
In general, according to the color that the lights emit, the aforementioned categories are divided into: White (W), Read (R) and Green (G).
In reality, it is necessary that the mariner knows the distance from which a light, whose characteristics are known to him, is going to appear. The course that has been shaped inside the area of visibility of the light, in combination with the speed of the vessel, provides an indication about the possibility of appearance of the light in the estimated time. If the light does not appear in the estimated time, this may signify the leeway of the vessel into a dangerous area. The delay of the appearance of the light may have been caused by an adverse current, whereas the sooner appearance of the light by a favorable current etc.
Luminous range of the light is called the maximum distance in nautical miles, in which its focal light can be visible having as a criterium the intensity of the illuminating device and the meteorological visibility in the area. The light’s and the observer’s height is not taken under consideration. The luminous range of the light, except from the lantern pane, depends on the illuminative power emitted by the device. As unit of measurement of the intensity of the light has been internationally established the candela CD, that corresponds to :
1 candela= 0,98 decimal candles or 0,97 British candles.
Geographical Range of the light is the maximum distance until which the focal light of the light can be visible when confined only by the Earth’s curvature and the observer’s height. The intensity of the light and the visibility in the area is not taken under consideration. Given that the Earth’s curvature is a stable element, it is obvious that the geographical range alters in accordance with the light’s and the observer’s height.
Nominal range is the maximum luminous range (distance) of the light, when the meteorological visibility in the area is 10 nautical miles. This is the range reported by nautical maps.
In Greece, a country with a large length of seashores there is an extended lighting network for the guidance of the mariners. There are 1400 lights and lighting buoys. All of them function automatically.
The service responsible for the installation, maintenance and function of the lighting network is the Service of Lighthouses of the Hellenic Navy, which, having under its authority two (2) vessels, and appropriately trained stuff, maintains and repairs the possible malfunctions that appear in the lighting network of the country.