What is a light novel?
Light novels (or Ranobe in Japanese) a type of short novels (published mainly in east Asia) that are usually marketed towards young adult audiences. The reason they're called light is due to their short length and easy vocabulary with anime-esque illustrations scattered along the text, so they're considered more 'accessible' than the average Japanese novel.
(some people call them 'anime in novel form' and that's probably the best way to describe them to the genre's newbies)

* note: some books that are considered novels in Japan, will be marketed as light novels in the west due to their young demographic/ anime artstyle. These will count in the challenge.
* note the second: due to the boom of popularity of LNs, not only have they been translated to many languages, but books outside of Japan can be called LNs if they have similar properties (ex. Seven Sea's publication of DanMei (Chinese genre that depicts romantic relationships between men) novels).