Whoops, nope. The last commit was a mistake.

It *seemed* to fix the problem I was running into, but it actually
made the SphereLight ray intersection code incorrect, and wa just
avoiding intersections that should have happened.

I should test better before committing. :-)

src/light/sphere_light.rs

@@ -227,7 +227,7 @@ impl<'a> Surface for SphereLight<'a> {
             let radius = lerp_slice(self.radii, r.time); // Radius of the sphere
 
             // Get the ray origin and direction in local space
-            let orig = (r.orig * xform).into_vector();
+            let orig = r.orig.into_vector();
             let dir = wr.dir * xform;
 
             // Code adapted to Rust from https://github.com/Tecla/Rayito