"A fully or partially enclosed built structure bearing a light that is used as a navigational aid and that is capable of admitting at least one person to operate or maintain the light entirely from within."
This is represented in the diagram shown in Figure 1.
The complete analysis of this subject is contained in a paper written in 2003 entitled Definitions and Usage of Terms Associated With Navigational Aids by Dr Ken Trethewey. In
this paper the author describes a precise set of definitions suitable
for use in pharology. In particular we learn how to distinguish various
kinds of navigational aids. The complete paper is contained in the following sections.