A filament (usually of multi-vee formation) in the form of a hollow circular cylinder generated around the axis of the lamp.
Note: The filament may be fully closed in plan, or may embrace an arc of less than 360 degrees.
The English term "Cylindrical filament" is usually limited to the case of a closed cylinder.
Otherwise, the English term used is "Bunch filament" (2-3-220).
Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)
International Association of Marine Aids to Navigation and Lighthouse Authorities - AISM