A noun is a word that names a person, place, thing, or idea. In this case, "lighthouse" names a structure that emits light to guide ships.
While you can't use "lighthouse" as a verb directly, you could use it in a metaphorical sense. For example, you might say:
* "He is a lighthouse of hope for the community."
In this case, "lighthouse" is used figuratively to describe the person's positive influence.