From my experience, light novel is the term western people use to refer Japanese novels. They are called light becos it doesn't contain much complex topics and character, oriented towards all age groups from kids to adults, this have easy to read wording and paragraph sometimes with manga like illustration to make it easy to realte to scene. They are often used for manga and anime adaption, or for side story of an popular manga.
Whereas novels are more diverse and have more pages than light novel. They cover all kinds of topics under sunlight and can be in any language not only Japanese.
Umm, well not that different but light novel is more orthodox novel, like they are printed and have professional people who have expertise in writing certain type of theme like Horror, suspense etc. are hired. Famous Japanese author, are hired for side story (of popular manga) novel adaptation, who can do justice to Manga. Tere are copyrighted and legal procedures n all involved in publishing. Novels can be shoujo, BL, fantasy, Even an anime called Hyouka is adapted from original novel-not based on anime. Light novels are purely Japanese, from names, kinks, settings, culture etc. where as Novel are as per the origin of country where it is written, means it can be from any country including Japan.
Whereas fanfic is novice work. Put in a site like Ffn and Watpad. Unless they are printed on pages and made into novel they can not be called light novel. I mean, as I am speaking from experience, I have never heard of E-light Novel..
Oh and if u r interested in reading them, I think this might be helpful :)
http://www.mangago.me/home/mangatopic/1758889/
What are light novels? Like, what's the difference between novels and light novels?
And can someone please recommend me a yaoi light novel, I'd love to read one!