what is the difference between light novels and manga
Manga are comics. The light novels in this case are the original source material, which means that any anime or manga you see of Haruhi Suzumiya will be adapted from the light novels. Each of the light novels has a few pictures (the first Haruhi light novel has 8 full color pages of pictures in the back). I have not read the Haruhi manga, but I would recommend the light novels if you are looking for something a bit different.