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Lesson 505 of 8807. Visual Fidelity and RenderingFree lesson

Utilizing Lumen Cards for Occlusion

Manually adjust Lumen cards to correct light leaking and ensure proper shadow occlusion in complex architectural interiors.

In this lesson, you will learn how to manually refine Lumen Cards to eliminate light leaking and ensure solid shadow occlusion in complex architectural interiors.

Understanding Lumen Cards

Lumen generates a simplified "card" representation of your scene to calculate global illumination and occlusion efficiently. Think of these cards as a low-resolution proxy shell wrapped around your meshes. When you face "light leaking"—where light bleeds through a solid wall or floor—it usually means the Lumen Cards aren't accurately representing the geometry, leaving gaps in the "watertight" volume the light tracer expects.

Visualizing the Problem

Before adjusting anything, you must see what the engine sees. Navigate to the viewport menu and select Visualize > Lumen > Mesh Cards. This displays the colored rectangular planes that Lumen uses to block light. If you see gaps between walls, floors, or ceiling meshes, light will leak through these seams.

Adjusting Card Generation

To fix these occlusion issues, you can modify how these cards are generated on a per-mesh basis:

  1. Open the Static Mesh Editor: Double-click your architectural asset.
  2. Lumen Settings: Locate the Lumen section in the Details panel.
  3. Max Lumen Mesh Cards: Increase this value if your mesh has complex geometry that the default card count (usually 6) fails to capture.
  4. Card Resolution: If increasing the count doesn't help, adjust the Card Resolution setting. A higher resolution allows for a tighter fit against the mesh, which is critical for thin architectural elements like window frames or door headers.
  5. Rebuild/Update: Sometimes, you need to toggle the Lumen Card Preview in the Mesh Editor to force a refresh of the card layout after changing settings.

If a specific mesh remains problematic, you can use the Lumen Scene View (Visualize > Lumen > Lumen Scene) to identify exactly where the occlusion is failing. If the cards are perfectly placed but leaking still occurs, ensure your meshes are snapped to a grid to avoid tiny gaps, as Lumen relies on the integrity of the mesh boundary to calculate shadow occlusion accurately.

Key Takeaway: Manually refining Lumen Mesh Cards by increasing card counts and resolution ensures a "watertight" proxy volume, effectively eliminating light leaks in architectural interiors.