Articles about engines - Nasty Rodent - Page 2

Question 1

What is Lumen in Unreal Engine 5?

Accepted Answer

Lumen is UE5's fully dynamic global illumination and reflections system. In supported UE5 rendering configurations, it serves as the default GI and reflections workflow for new projects, allowing indirect lighting, bounce light, color bleed, emissive material contribution, and reflections to update in real time — without precomputed lightmaps or rebuild passes.

Question 2

How is Lumen different from baked lighting?

Accepted Answer

Baked lighting (Lightmass) precomputes indirect light into static lightmap textures — fast at runtime, but locked to static geometry and requiring hours of build time. Lumen calculates GI dynamically every frame using ray tracing methods. The key production differences: no lightmap UV channels needed, instant iteration, support for dynamic scenes and time-of-day, but higher runtime cost and limited support for legacy platforms.

Question 3

Does Lumen work on all platforms?

Accepted Answer

No. Lumen targets next-generation consoles (PS5, Xbox Series X/S) and high-end PC. It is not available on PS4 or Xbox One. VR projects typically require a non-Lumen lighting path due to performance and rendering-path constraints. Limited mobile support exists for specific high-end Android devices with Vulkan SM5. Projects targeting legacy hardware need a non-Lumen lighting path.

Question 4

What is the difference between Software and Hardware Ray Tracing in Lumen?

Accepted Answer

Software Ray Tracing uses Mesh Distance Fields and is the broadest-compatible Lumen path — available across the widest range of UE5-supported hardware, though still subject to feature level and scalability settings. Lower accuracy on thin or complex geometry, 200m default scene coverage. Hardware Ray Tracing uses dedicated RT cores for higher-accuracy BVH intersection — better reflections, better skinned mesh support, further GI coverage, but requires DX12-compatible hardware and carries a higher performance cost.

Question 5

What are Lumen's limitations for environment artists?

Accepted Answer

The key limitations: Lumen has limited support for translucency — glass, water, and particles do not fully participate in GI/reflection tracing; large emissive surfaces increase tracing cost; Lumen is incompatible with Forward Shading; and it cannot be mixed with traditional baked lightmaps in the same project. For environment art, meshes need clean topology and proper Distance Field generation — poorly closed meshes or very thin geometry can generate incorrect indirect lighting results.

Question 6

When should you use baked lighting instead of Lumen in UE5?

Accepted Answer

Baked lighting remains the better choice when targeting legacy platforms (PS4, Xbox One, Switch), building for VR, targeting high frame rates where GI cost cannot be budgeted, or working on mobile productions outside Lumen's supported device range. Productions with heavy translucency — water, glass-heavy environments, particle-dominant visual styles — should also evaluate whether Lumen's translucency limitations create unacceptable visual gaps before committing to a Lumen-based pipeline.

Blog - Page 2

What Is Lumen in Unreal Engine 5: Real-Time Global Illumination Explained

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What Is Nanite in Unreal Engine 5: A Technical Guide for 3D Production Teams