A cap (type P) which enables the luminous element to be brought into a specified position relative to the cap during manufacture of the lamp.
By this means, reproducible positioning can be assured when the lamp is inserted in a suitable lampholder.
Note: A Flanged Cap (Culot a Ailettes in French; Flanschsockel in German) is a particular type of pre-focus cap.
Reference: C.I.E. (modified)
Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)
Celsius (previously Centigrade)
International Association of Marine Aids to Navigation and Lighthouse Authorities - AISM