Troubleshooting Common Lumen Artifacts

Diagnose and resolve common visual issues like splotchiness, light leaking, or ghosting by adjusting project-wide Lumen parameters.

In this lesson, you will learn how to identify the causes of common Lumen artifacts like splotchiness, light leaking, and ghosting, and how to resolve them through global project settings.

As Lumen relies on a combination of Surface Cache and Mesh Distance Fields, artifacts often arise when the lighting engine struggles to calculate stable radiance in complex or thin geometries.

Resolving Splotchiness and Noise

"Splotchy" lighting usually occurs when the Surface Cache has insufficient resolution to capture fine detail, or when the Final Gather quality is set too low. If your walls look blotchy, navigate to your Post Process Volume and increase the Lumen Scene Quality. This forces the engine to allocate more resources to the scene representation. If the splotches persist during movement, check your Lumen Final Gather Quality; increasing this value reduces temporal noise but comes at a higher GPU cost.

Fixing Light Leaking

Light leaking typically happens when geometry is too thin or not manifold (watertight). Because Lumen uses Distance Fields for global illumination, it may treat thin walls as "transparent" to light rays.

Check the Distance Field: Use the Visualize > Mesh Distance Fields view mode to ensure your mesh has a clean representation.
Adjusting Bias: If the leak is persistent, you can tweak the Distance Field Resolution Scale on the mesh component itself to refine the occluder. For global fixes, ensure Lumen Scene Lighting Quality is high enough to capture the contact shadows that hide these leaks.

Addressing Ghosting

Ghosting occurs when Lumen's temporal accumulation fails to settle quickly after a camera move or dynamic light change. This is most common in fast-paced scenes or with high-intensity emissive surfaces. To mitigate this, check your Project Settings > Rendering > Lumen and ensure the Lumen Scene Update Speed is tuned appropriately. If ghosting is severe, you may need to increase the Lumen Scene Lighting Update Speed or reconsider the use of high-intensity emissive materials that update too rapidly for the temporal filter to resolve.

Key Takeaway: Most Lumen artifacts stem from insufficient Surface Cache resolution or temporal instability; prioritize refining your Mesh Distance Fields and Post Process Quality settings before adjusting individual asset overrides.