Well, webnovels tend to be more diverse in terms of genre and length. They can range from short stories to extremely long epics. Also, the writing style might be more straightforward as they are aimed at a wide online readership. Light novels are more focused on a particular aesthetic that is associated with Japanese pop culture. Their plots are sometimes more in line with the common tropes in anime and manga, like high school settings, magical powers, and cute characters.
Webnovels have a global reach as the internet allows them to be accessed from all over the world. They can be updated frequently, and readers can often interact with the authors through comments. Light novels are deeply rooted in the Japanese publishing industry. They have a different marketing and distribution model. For example, a successful light novel might get adapted into an anime or a video game, which further promotes its popularity. The cover art and internal illustrations in light novels are an important part of their appeal, which is not as emphasized in webnovels.