Lumen is scalable, and supports a wide range of DX11 and DX12-capable hardware using Software and Hardware Ray Tracing modes. Valley of the Ancient uses Software Ray Tracing, which combines Screen Traces (or screen space tracing) with a Surface Cache representation to generate indirect lighting in the scene. Lumen uses Screen Traces to cover the mismatch that can happen with the lower quality Surface Cache, which is generated from the individual mesh's Signed Distance Field. You can visualize the Surface Cache using Show > Visualize > Lumen Scene. The Surface Cache only operates for the first 200 meters before falling back to screen traces for the distance scene.
Lumen is versatile and has quality options that enable it to work with both Nanite's virtualized geometry and traditional Static Mesh geometry, and screen traces enable skinned meshes to receive and contribute to indirect lighting, but they are limited by what's visible on screen. You can visualize Lumen's combined techniques by clicking Show > Visualize > Lumen Global Illumination inside an editor viewport.
