Unreal Lumen: choose tracing and quality around the scene you must render

Define the lighting requirement

Lumen supplies dynamic diffuse indirect lighting and reflections, and those two features can be selected independently. [1] Start by describing what must change during play: a door opening onto daylight, a moving reflective object or an emissive sign switching off. That description creates a testable requirement. A lighting system should be evaluated against these changes, not only a carefully composed still image.

Choose a tracing representation

Software tracing uses distance fields; hardware tracing can intersect triangles and supports additional geometry such as skinned meshes. Screen traces also contribute to the result. [2] Choose according to target hardware and scene requirements, then inspect the representation actually used. Hardware availability alone does not prove that the more expensive option improves the particular shot you care about.

Budget quality as a system

Lumen quality depends on scalability, resolution and scene structure. Hardware tracing costs are sensitive to overlapping geometry; smooth reflective surfaces can add significant reflection work. [3] Compare settings with the same camera route, internal resolution and upscaling configuration. Record both visual failures and frame time. A preset name is a starting configuration, not a guarantee of a particular frame rate on your content.

Example: a museum after closing

Imagine a museum where security shutters close over a bright courtyard and a moving exhibit passes a polished wall. Build one repeatable sequence: hold the camera still, close the shutters, move the exhibit and then turn away from the reflective wall. Observe how indirect illumination settles and whether the moving exhibit remains represented in reflections. Compare the supported tracing options on target devices with the same scene and quality settings. If a reflection changes when its source leaves the screen, inspect the screen-trace contribution and the underlying scene representation before increasing every quality setting. This is an original diagnostic scenario, not evidence that a particular device reaches a performance target.

Limits and useful checks

The referenced technical documentation excludes Forward Shading and describes distance-field problems with thin geometry. [2] Match these requirements to the project’s engine version. Inspect Lumen’s scene and surface-cache views when walls leak light or reflected objects disappear. Check geometry, material setup and representation coverage before adding compensating lights. Include rapid camera motion and abrupt lighting changes in acceptance tests, because temporal behaviour matters. For each target configuration, define an acceptable fallback and confirm both its image and cost rather than relying on automatic selection alone.

Sources

1. Lumen Global Illumination and Reflections — Epic Games.
2. Lumen Technical Details — Epic Games.
3. Lumen Performance Guide — Epic Games.