Unreal Engine 5 Lumen Guide: Interior Lighting and Performance Settings

Epic Games’ official Lumen documentation for Unreal Engine 5 explains how to enable real-time global illumination and reflections, and scale them for performance. Lumen dynamically calculates indirect light bouncing off surfaces, color bleeding, and reflections. The steps below offer a documentation-based starting point for balancing lighting quality and performance, especially in interior scenes.

1. Enable Lumen correctly in your project

Lumen’s global illumination and reflections are enabled by default in newly created projects. In projects converted from Unreal Engine 4 to Unreal Engine 5, however, the setting is not enabled automatically. Start by checking your project settings.

1. Open Project Settings and go to the Dynamic Global Illumination category under Rendering.

2. Set Dynamic Global Illumination Method to Lumen.

3. In the Reflections category, set Reflection Method to Lumen. Global illumination and reflections can be configured separately, so check both.

4. If you’re using software ray tracing, make sure Generate Mesh Distance Fields is enabled. This feature is required for Lumen’s Software Ray Tracing mode; the engine must be restarted after enabling it.

When Lumen is enabled, precomputed static lighting contributions are disabled and lightmaps are hidden. Lumen replaces Distance Field Ambient Occlusion and Screen Space Reflections. So, in a converted project, review the scene rather than assuming the previous lighting setup will work in the same way.

2. Balance interior lighting and reflections for your scene

Lumen Global Illumination lets indirect light carry surface colors and creates indirect shadows from objects in the scene. The system supports an unlimited number of diffuse light bounces. Sky lighting also contributes to the Final Gather process, which can help interiors appear darker than exteriors.

1. After setting up the scene’s basic lighting, review the Global Illumination and Reflections categories in Post Process Volume.

2. Increasing Final Gather Quality can reduce noise and improve global illumination quality, but it also increases GPU cost. Evaluate the image at the current value first, then raise it as needed.

3. Use Lumen Scene Detail and Lumen Scene View Distance to adjust how small objects are represented and how far lighting is traced. Higher values can provide more detail or range, but may increase cost.

4. In reflections, the Quality setting improves quality and reduces noise, but increases GPU load. Lumen uses special reflection rays on glossy surfaces with low roughness; the amount of these surfaces in the scene affects cost.

According to the documentation, pixels with a roughness value below 0.4 use special reflection rays by default. You can change this threshold with Max Roughness To Trace. Lowering the threshold may mean fewer pixels use special rays, but reflection quality may change as a result. Evaluate the setting based on the surfaces that actually need it in your image.

3. Choose a quality level and ray tracing method

Unreal Engine’s Lumen quality levels offer different performance costs depending on your target. Epic’s Epic level targets 30 fps on consoles, while High targets 60 fps on current-generation consoles. Medium is specified for Switch 2 and mid-range PCs, while Low disables Lumen features. Each lower quality level costs approximately half as much as the level above it.

You can access the quality options via Viewport-related Settings > Viewport Scalability Settings in the Level Editor. Epic notes that quality groups can also be controlled through console profiles. Hardware ray tracing can deliver higher quality, but it costs more and is sensitive to overlapping geometry. Epic’s performance guide for current-generation consoles gives fewer than 100,000 instances after culling in a ray tracing scene as a general performance target; this is not a fixed limit for every Windows system.

4. What to consider in an architectural visualization workflow

In interior and architectural scenes, Lumen’s dynamic indirect lighting lets you see surface colors reflected onto their surroundings and shadows forming in shaded areas. This can be useful when evaluating material, lighting, and camera decisions in the scene. However, since higher-quality settings increase GPU cost, choosing the highest level for every scene may not be the right approach.

First, check the scene’s basic appearance and performance with software ray tracing. When moving to hardware ray tracing, review the number of instances in the scene and any large or multilayered overlapping meshes. Epic notes that disabling ray tracing visibility for meshes that cover a large area, such as a skybox, can reduce cost. Since statically set lights are not supported when Lumen is enabled, also verify the Mobility values of your lights.

Common mistakes

• Assuming Lumen is enabled automatically in a project converted from Unreal Engine 4.

• Forgetting that the engine must be restarted after enabling Generate Mesh Distance Fields.

• Expecting static lights to continue contributing when Lumen is enabled.

• Increasing quality for hardware ray tracing without checking overlapping meshes and the number of instances in the scene.

• Overlooking the potential increase in GPU cost when raising reflection and Final Gather quality.

These settings are based on Epic’s Unreal Engine 5 Lumen documentation. As the documentation does not specify a minor version number, this guide cannot be tied to a specific version number.