Greifswalder Oie lighthouse is well known. I was surprised to find ARLHS FED-355 in ARLHS list. This small tower is known as old fog horn! Was it lighted someday? A coal fire ?
Sometimes foghorns (unlit) are shown in the Admiralty list of lights separately under own number. Maybe ARLHS is doing the same?
Webside http://www.deutsche-leuchtfeuer.de/index.html (http://www.deutsche-leuchtfeuer.de/index.html) : old coal fire from 1832-1855 ! But why listed in ARLHS ?
Here might be the solution: http://www.baken-net.de/image/groie1832.jpg (http://www.baken-net.de/image/groie1832.jpg)
Short translation: The tower had 2 lanterns with a spherical headlight, in the middle was an Argand lamp.
First time I have heard from an Argand lamp, which is working with oil! ;)
Amazing how much archive data is available now in web :)