Published on 15 February 2008
old dome at the Triagoz-Côtes d'Armor.
old dome at the Triagoz-Côtes d’Armor.
(Source: Dreyer-Damgm)

After 1770, lanterns became bigger, resulting from the use of metal lamps. They then had a (average) diameter of 12 ft (about 4 metres) and rested on a low, circular brick wall. The dome was made with repoussé copper panes, topped with a ball holding the chimneys. They were fitted with little mirrors mounted plumb on metal frames.

Lanterns were re-classified by Augustin Fresnel. Their sizes were established according to the rated range “ordre” of the light:

{{}} 1st classification 2nd classification 3rd classification 4th classification
Focal point of optic (in metres) 0.90 m 0.70 m 0.50 m 0.30 m
Diameter 3.5m 3m 2.5m 1.6m/1.4m
Number of panes 16 12 10 8
Height of glazing 3m 2.7m 2.25m 1.4m
Height of supporting wall 2.2m 2.1m 2m 0.9m
old dome at the Department of Lighthouses and Beacons at the Trocadero in Paris.
old dome at the Department of Lighthouses and Beacons at the Trocadero in Paris.
(Source: Dreyer-Damgm)

This method of classification is no longer in use today.

The small brick wall disappeared around 1850/1860, to be replaced by a metal base, initially in iron and bronze or riveted copper. After 1910, the manufacturing processes in the metallurgical industry allowed the big base cylinders to be made in one piece.

In the post-war reconstruction, lanterns were standardised by A. de Rouville the Director of Lighthouses at the time, who limited the number of models. Two large French manufacturers, Barbier Benard and Turenne and Sutter-Harlé or Sautter-Lemonier, made this equipment.