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History of lighthouses in Mauritius
Several lighthouses were built during Mauritius' colony period in the 18th century to aid ships in navigating the sea. This resulted in an increase in the pace of import and export, resulting in a boom in trading on the island. Because of its strategic location on the map, Mauritius was regarded as a vital commercial hub, attracting several European governments during colonial expansion. Because ships were the only way to trade over the ocean, lighthouses played a crucial role in the process.
The lighthouse, sentinel of the sea
The lighthouse, a stone giant exposed to the elements, sometimes isolated in the middle of the sea, nevertheless reassures sailors in the dark. It guides ships to port and has saved many ships in perdition. And yet, we know little about this solitary sentinel. Derived from Pharos, the name of the ancient island (now a peninsula) on which the lighthouse of Alexandria stood, the lighthouse was born with the rise of maritime trade. Originally, it was a system designed to signal the coast at night, but it was soon realized that even more could be done with a lighthouse.
The history of the lighthouse in the world
As early as antiquity, lights were lit to signal the land to approaching ships at night. These were first lit high up on the coast, but very soon platforms were built to improve visibility, and finally towers were built. These were often built very high to serve as landmarks (fixed and recognizable points of reference) during the day and to be seen from afar when they were illuminated at night.
The primary role of the lighthouse is to indicate to the navigator the proximity of the land. If they are placed at the entrance to a harbor (a red lighthouse and a green lighthouse), they unambiguously signal the entrance to the harbor and a safe path to the roadstead. But a lighthouse is not always built on the mainland. Some are useful on the high seas or on an island, to mark a safe route for example, or to signal a particularly dangerous area. They thus become an essential element for the safety of navigation. Unfortunately, the advent of modern tracking systems and recent technological advances in this field have made lighthouses obsolete. Today, they are either automated or gradually abandoned, or even transformed into tourists hotels or guesthouses. As a result, there are only 1,500 lighthouses left in service in the world.
The structure of a lighthouse
A lighthouse is generally composed of a tower, more or less high, and an optical system. The tower can be built to withstand bad weather, gusts of wind, the onslaught of the sea, storms and other gusts. This is why a lighthouse is most often circular, even if there are octagonal or hexagonal lighthouses, or even square ones. Some are even mounted on pylons or on a boat!
The optical system is placed at the top of the tower and produces the desired light. It includes a powerful light source and special lenses, called Fresnel lenses. These were designed to concentrate the light as much as possible.
The lighting systems of the lighthouse
To produce its light, the lighthouse can use different kinds of energy sources. In the 18th century, wood was used as the main source of energy and was very expensive. This is why lighthouses were only lit when a ship was approaching. This system was then replaced by coal and then by the oil lamp with silver-plated copper reflectors.
Towards the end of the 20th century, oil took over, in parallel with the incandescent mantle whose high light power associated with Fresnel lenses allowed to increase enormously the efficiency of lighthouses. With modernization, however, most lighthouses began to operate with electricity. For a time, the USSR used nuclear power to power its lighthouses. Today, this technique causes real environmental and safety problems. A question of light and range
To be useful, a lighthouse must be visible from as far away as possible and in all weather conditions. Thus, everything is designed to optimize its light.
To begin with, the range of the beam projected by the headlight depends on its power and height. We can thus classify headlights in 3 categories:
- Third-order headlights, with a range of 28 km
- Second-order headlights, with a range of 40 km
- First order lighthouses, with a range of 60 km
Then, to avoid scattering, the light of the lighthouse is flattened horizontally to carry as far as possible and sweeps the horizon intermittently. However, to avoid confusion, each lighthouse must have its own characteristics, grouped under the term "light signature". This signature is composed of the color of the light signal, the sequence of light pulses and darkness phases, and finally the duration of this sequence. The light signatures of each lighthouse in the world are available in "light books", published by each country for the use of navigators.