Many of the published definitions for the term "lighthouse" are inadequate in today's context.
A precise definition of a lighthouse is:
"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 the paper: Definitions and Usage of Terms Associated With Navigational Aids by Dr Ken Trethewey (2003)
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 presented in a more convenient format in the following sections.
This work has also been published in:
Ken Trethewey, "What Is A Lighthouse? A Modern Definition". World Lighthouse Society Magazine, 1st Quarter 2013, Volume 11, Issue 1, p5-14 available at www.worldlighthouses.org