Lumen & Nanite in UE5
What the parent explanation assumed you knew:
You understand that Unreal Engine 5 renders MetaHumans with advanced lighting and detail, but not the specific technologies involved.
What this page explains:
How Lumen provides dynamic global illumination and Nanite handles virtualized geometry, including their limitations with MetaHumans.
The Explanation
Unreal Engine 5 introduced two revolutionary rendering technologies. Understanding their capabilities and limitations is essential for MetaHuman optimization.
Lumen: Dynamic Global Illumination
Lumen provides real-time indirect lighting without baking:
How It Works:
1. Surface Cache: Pre-render low-res views of all surfaces 2. Ray Tracing: Trace rays from camera to find lit surfaces 3. Gather Lighting: Sample the surface cache for indirect light 4. Temporal Accumulation: Spread computation across frames
For each pixel:
1. Cast ray into scene
2. Hit surface → lookup surface cache
3. Surface cache contains: albedo, normal, emissive, indirect lighting
4. Combine direct + indirect lighting
5. Accumulate over multiple frames for stabilityLumen Modes:
| Mode | Quality | Performance | Use Case | |------|---------|-------------|----------| | Software | Good | Faster | No RTX GPU | | Hardware RT | Excellent | Slower | RTX GPUs, film quality |
**MetaHuman + Lumen:**
- •Skin subsurface scattering works beautifully
- •Eye caustics render correctly
- •Hair may need special handling
- •Performance cost is significant
---
Nanite: Virtualized Geometry
Nanite streams and renders billions of triangles efficiently:
How It Works:
1. Clustering: Pre-process mesh into hierarchical clusters 2. LOD Selection: GPU chooses detail level per cluster based on screen size 3. Visibility: Software rasterization culls invisible clusters 4. Rendering: Only visible, appropriately-detailed clusters drawn
Mesh (10M triangles)
↓
Cluster Hierarchy (LOD 0-8)
↓
GPU selects visible clusters at appropriate LOD
↓
Render only what's needed (~100K triangles visible)Nanite Limitations:
**Cannot handle:**
- •Skeletal meshes (animated bones)
- •Morph targets (blendshapes)
- •Per-vertex animation
- •Translucent materials
- •Two-sided foliage
MetaHuman + Nanite: NOT COMPATIBLE
MetaHumans are skeletal meshes with blendshapes. Nanite cannot be used for:
- •Face mesh
- •Body mesh
- •Clothing (if rigged)
Nanite CAN be used for:
- •Static environment
- •Props
- •Non-animated elements
---
MetaHuman Rendering Strategy:
┌─────────────────────────────────────────┐
│ MetaHuman Rendering │
├─────────────────────────────────────────┤
│ Face/Body: Traditional skeletal mesh │
│ - LOD system (0-7) │
│ - ~700 bones at LOD 0 │
│ - Blendshapes for expressions │
│ │
│ Hair: Two options │
│ - Strands (ray-traced, expensive) │
│ - Cards (faster, lower quality) │
│ │
│ Lighting: Lumen │
│ - Subsurface scattering │
│ - Eye reflections │
│ - Dynamic shadows │
├─────────────────────────────────────────┤
│ Environment: Nanite │
│ - Static geometry │
│ - Billions of polygons │
│ - Automatic LOD │
└─────────────────────────────────────────┘Performance Budgeting:
Target: 60 FPS, 16.67ms per frameTypical MetaHuman budget: - Skeletal evaluation: 1-2ms - Face rendering: 2-3ms - Hair (strands): 3-5ms - Lumen GI: 2-4ms - Post-processing: 1-2ms ───────────────────── Total: 9-16ms (leaves margin)
With 10 MetaHumans:
- Multiply skeletal/face costs
- May need to use hair cards
- Consider LOD distance settings
`
Optimization Recommendations:
1. Use LOD aggressively (LOD 2-3 for background characters) 2. Switch to hair cards when performance-critical 3. Limit Lumen ray budget in dense scenes 4. Use Screen Percentage scaling under load
Visual Aid
Toggle Lumen/Nanite settings and see their effect on visual quality and performance.
Open interactive demo →The "Aha" Moment
Lumen makes lighting dynamic, Nanite makes geometry infinite - but MetaHumans can only use Lumen because animated characters need traditional skeletal rendering.
Go Even Deeper
This explanation assumes you understand these fundamentals. Click to learn more:
ray tracing basics
Level 1 fundamental
lod systems
Level 1 fundamental