A lens (in sense 2 of 2-2-010) made up of a belt of lenticular section and a series of rings of prismatic section above and below it.
The axes of revolution of the belt and rings form the same vertical straight line.
The rings are contiguous or nearly so.
Note 1: A fixed lens need not extend through 360 degrees, but may be limited to a sector.
Note 2: The light issuing from a fixed lens is in the form of a fan beam (2-1-090).
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