Lumen was the Unreal Engine lighting technology cited during Halo Studios’ engine change.
Halo Studios shifted development from its proprietary Slipspace Engine to Unreal Engine 5 for Halo: Campaign Evolved. In the discussion of that change, Lumen was identified as a major opportunity because it can calculate dynamic global illumination and reflections as scenes change, rather than relying only on lighting that was prepared in advance.
Lumen is not a physics system, foliage tool, or legacy Halo technology. SpeedTree is associated with vegetation, PhysX with physics middleware, and Havok with physics and related simulation tools. Those technologies may appear in game-development conversations, but they are not the lighting feature named here.
Lumen is also frequently paired with Nanite, another Unreal Engine 5 feature used by Campaign Evolved. The distinction is useful: Lumen concerns how light and reflections behave, while Nanite concerns the presentation of highly detailed geometry. Together, they helped support the remake’s more elaborate environments and visual effects.