Setting Up Lumen and Hardware Ray Tracing for Archviz in Unreal Engine

What will you learn in this guide?

Lumen is Unreal Engine’s dynamic global illumination and reflection system. In architectural visualization scenes, it can be used to examine indirect light moving between surfaces, color bleeding, and reflections. This guide walks through Lumen’s project settings, the Mesh Distance Fields option required for software ray tracing, and how to configure hardware ray tracing.

In interior visualizations, daylight, glossy surfaces, and the shadows cast by artificial lights are considered together. These settings can affect both image quality and performance costs. The goal, therefore, is not to set every option to its maximum, but to test the look your project needs in the scene you’re working with.

Requirements and before you begin

The source documents do not specify a particular Unreal Engine version, graphics card model, or compute requirement. Hardware ray tracing requires a compatible graphics card, RHI, and operating system. When the feature is enabled, Unreal Engine may recommend enabling Support Compute Skin Cache; hardware ray tracing requires this option to be enabled.

Lumen is enabled by default for global illumination and reflections in newly created projects. In projects converted from Unreal Engine 4 to Unreal Engine 5, however, Lumen is not enabled automatically. This behavior prevents a project’s existing lighting setup from changing automatically.

Lumen’s software ray tracing requires Generate Mesh Distance Fields. Enabling this option requires restarting the engine. Generating Mesh Distance Fields can increase static mesh build times, memory usage, and disk size. Before making changes, also check the project’s existing lighting setup: when Lumen is enabled, precomputed static lighting contributions are disabled and lightmaps are hidden.

Enabling Lumen and reflections

1. In Project Settings, find the Dynamic Global Illumination and Reflections categories under Rendering. The methods in these categories are configured independently.

2. Select Lumen for Dynamic Global Illumination and Lumen for Reflection Method. Changing only one does not automatically switch the other to Lumen.

3. If you plan to use software ray tracing, enable Generate Mesh Distance Fields. Restart the engine after making this change.

4. Check the indirect light and reflections in your scene. Lumen can make light reflected from a surface pick up that surface’s color and carry it to nearby surfaces. This effect appears as color bleeding.

Sky lighting is calculated during Lumen’s Final Gather process. According to the source document, this process also includes sky shadows, so interiors can remain darker than exteriors. When comparing lighting, observe the relationship between indoor and outdoor areas, color bleeding, and reflections together.

Lumen supports directional, sky, point, spot, and rectangle lights. Lights set to Static are not supported because static lighting contributions are stored in lightmaps and are disabled when Lumen is enabled. Check the mobility settings of existing lights and whether the project relies on precomputed lighting.

Configuring hardware ray tracing

1. In Project Settings, go to Engine > Rendering > Hardware Ray Tracing and enable Support Hardware Ray Tracing. If needed, enable Support Compute Skin Cache as well.

2. In the Lumen settings, check Use Hardware Ray Tracing when available. If the hardware, RHI, or operating system does not support it, Lumen falls back to software ray tracing.

3. For Lumen to use hardware ray tracing, also set Ray Lighting Mode to Hit Lighting for Reflections. Surface Cache prioritizes performance by using lighting information from cards generated by Lumen for reflections. Hit Lighting for Reflections calculates lighting at the point where the ray hits and can provide higher-quality reflections, but GPU costs increase significantly in return.

4. Review the Lumen options in the Post Process Volume for your scene. Lumen Scene Lighting Quality, Final Gather Quality, and reflection Quality settings can help improve quality; each can also increase GPU costs.

Hardware ray tracing works alongside traditional raster techniques for supported features. Epic Games warns that Lumen hardware ray tracing can incur significant scene update costs in scenes with more than 100,000 instances. In large scenes, therefore, don’t choose settings based on quality expectations alone; compare the results using your target camera and content.

Common mistakes and their impact on archviz workflows

Enabling hardware ray tracing does not mean all Lumen settings automatically switch to their highest quality. For Lumen to use hardware ray tracing, both Use Hardware Ray Tracing when available and Hit Lighting for Reflections under Ray Lighting Mode must be set. If compatibility requirements are not met, the system may fall back to software ray tracing.

You may also run into problems if you enable Mesh Distance Fields for software ray tracing but forget to restart the engine. Also account for the effect these fields have on build times, memory, and disk usage, as well as the fact that static lighting contributions are disabled when Lumen is enabled. Keep in mind, too, that Lumen is not enabled automatically in projects converted from Unreal Engine 4 to Unreal Engine 5.

Architects, interior designers, and archviz artists can use Lumen to inspect indirect light, color bleeding, and reflections in real time. Hardware ray tracing, however, requires a compatible graphics card, RHI, and operating system; options such as Hit Lighting for Reflections can increase GPU costs. Before sharing project settings with your team, check compatibility on target systems and compare quality and performance in your scene.

Next steps

First, evaluate how your scene looks with the Lumen settings currently applied to the project. If you need to enable hardware ray tracing, configure the required options together and examine the effect of the reflection mode. Testing one option at a time when adjusting quality settings makes it easier to track visual differences.

During comparisons, pay particular attention to sky lighting in interiors, reflective surfaces, light types, and the mobility settings of lights. In large scenes, also consider the number of instances. This will help you assess more systematically how quality improvements affect GPU costs and the project’s existing lighting setup.

Source and license

This content has been adapted into Turkish from Epic Games’ “Lumen Global Illumination and Reflections” and “Hardware Ray Tracing in Unreal Engine” documents. Both sources are offered under free licenses.