Well, can you read Japanese? The light novels don't have any translations in English besides the first half of Volume 1-A, the first third of volume 3-A and a few chapters here and there (There might be translations in Chinese though, if you can speak that). So if you can't read Japanese, you'll likely have no choice but to watch the anime anyway.
This isn't bad though as the anime is a really good adaptation, notably did a good job at condensing the rather dense novels and presenting it in a way that does not require knowledge of the source material to enjoy it (although some parts in the second season don't make as much sense if you haven't read the novels). It also had an amazing VA cast, good animation and one of the best OSTs ever (although Horizon is my favorite anime/light novel series so I'm extremely biased towards it as whole); I would really recommend you to watch it even if you decide to read the light novels.