Glass for ship lights
The Fresnel lens is the characteristic lens for ship lamps for navigation lighting. It was invented by Augustin Jean Fresnel around 1770 and has been named the invention that saved a million ships.
This was predominantly due to its use in lighthouses. In the 1820s, Augustin Fresnel invented a new kind of lens and installed it in France’s Cordouan lighthouse.
Suddenly, one lamp could light the way for sailors many miles out to sea.
Ship lights have mostly convex Fresnel lenses. A significant advantage of a Fresnel lens is that less material is needed, which ensures weight savings without compromising efficiency.
Genthe Glass Goslar GGG
This is the logo of the German company Genthe Glass from Goslar. Genthe Glass Goslar was founded in 1926 and went bankrupt in 2008. Many ship lights with Fresnel lenses have a triangle with the letters GGG in the glass.
Chance Brothers, C.B. LTD. England
Chance Brothers from Smethwick was an English glass manufacturer of ship lamps. It was a leading glass manufacturer and a pioneer of British glassmaking technology.
The company was founded in 1822, and from 1851 it became a significant lighthouse engineering company. They also produced Fresnel lenses for ship lights, but you don't see them as often as Genthe Glass.
Change brothers later became Chance Glass Limited, which is still in business and based in Malvern Link.
Numbers engraved in the glass of ship lights
Numbers are often engraved in the glass of ship lamps; inspection numbers indicate that the lens and ship light were approved. A certificate was given for the ship's lamp. Who inspected the ship lights differed per country. Follow this link if you wish to read more about ship light certification per country.
I could provide you this article partly thanks to the following sources: