It's not strictly speaking a "scene description language", it just looks like that at first glance.

It's a fully capable compiled programming language, which I happen to have written a raytracer in. Check out the "pathtrace" tab.

The advantage is if there's some issue with the raytracer, you can fix it yourself. And you can use arbitrary scripts for making scenes. (Though the scene in memory must not exceed 32MB, which may limit you somewhat.)