General info about lighthouses

A few centuries ago coastal shipping could only navigate during the day and had to anchor before nightfall. So there was little need for lighthouses. Trade and commerce changed all that, so need became the mother of invention.

 

A lighthouse has 3 functions:

* It defines a particular spot on the coastline
* It helps the ships to navigate
* It marks the dangers that cannot be seen (for example: rocks under the water)

 

Literary Definition

Lighthouse: masculine (comes from Greek Pharos) a tower built on the coastline or on an island and equipped with a light to guide the ships in the night.

 

Technical Definition

It is a maritime object for navigation that consists of 4 elements:

* A tower located above sea level, mostly located along the coastline
* A lamp producing light
* An optical system to magnify the light to the horizon
* A lantern to protect the lamp and optical system

 

The nominal range of a lighthouse

The nominal range of a lighthouse is the distance at which the navigator can see the lighthouse. The range doesn’t only depend on the height where the light is placed but also the height of where the navigator is.

 

The range of the light

The range of the light of a lighthouse is the distance at which the light can be seen by the navigator. It depends on the power of the lamp and the weather (rain, night, fog,…etc.), that is why the light is given a nominal range based on clear conditions. Some lights will have nominal range that is less than the range at which the light can be seen and this will be due to the curvature of the earth. At 27 miles the curvature of the earth begins to take effect on the distance at which an object or light can be seen.

 

Criteria according to the “Bureau des phares et Balises”

1. A lighthouse is an establishment that full fills 2 of the 4 criteria: (this is not a universal definition)
2. A beacon is a light that full fills 1 criteria.


* Function: Placed where there are known hazards to navigation.
* The height: an establishment that is higher than 20m above sea level
* The intensity: the intensity of the light has to be powerful enough. (more than 100000 candelas: a candela being the equivalent of the power of one candle)
* The infrastructure: Designated so by “Le Bureau des phares et Balises”.


Lighthouse can be classified in 4 categories:

* First order: these indicate the approach of the land
* Second and third order: these signalize the dangerous passages and reefs
* Fourth order: that are lighthouses that indicate the entrance of the harbour

 

The French lighthouse keepers classify the lighthouses in 3 categories:

* “Hell”: that are lighthouses that are located in the sea
* “Purgatory”: these are also located in sea but on an island
* “Paradise”: these are located on land

 

Automisation

Because the lighthouses at sea became more difficult to reach they started automate those lighthouses in 1967.