Lumen
Take a look at a high-level overview of Lumen's dynamic global illumination and reflections features.
Last updated
Take a look at a high-level overview of Lumen's dynamic global illumination and reflections features.
Last updated
Lumen is Unreal Engine 5's fully dynamic global illumination and reflections system that is designed for next-generation consoles, and it is the default global illumination and reflections system. Lumen renders diffuse interreflection with infinite bounces and indirect specular reflections in large, detailed environments at scales ranging from millimeters to kilometers.
Lumen brings robust dynamic global illumination to Unreal Engine and integrates well with other supporting systems in Unreal Engine 5, such as Nanite, World Partition, and Virtual Shadow Maps.
Unreal Engine 4 features, like Screen Space Global Illumination and Ray Tracing Global Illumination (RTGI) were not reliable or performant for projects that relied on real-time with a high enough quality. Also, these features did not fully integrate with other important systems to widely support most features of the engine.
Lumen Global Illumination solves diffuse indirect lighting. For example, light bouncing diffusely off a surface picks up the color of that surface and reflects the colored light onto other nearby surfaces — creating an effect called color bleed. Meshes in the scene also block indirect lighting, which also produces indirect shadowing.
Lumen provides infinite diffuse bounces, which are important in scenes with bright diffuse materials like the white paint in the apartment below.
Sky lighting is solved as part of Lumen's Final Gather process. It includes sky shadowing, allowing indoor space to be much darker than outdoor lighting, providing a much more natural effect.
Lumen also provides lower-quality global illumination for Lit Translucency and Volumetric Fog.
Emissive materials propagate light through Lumen's Final Gather with no additional performance cost. However, there's a limit to how small and bright emissive areas can be before they begin to cause noise artifacts to appear. It is inherently much more difficult to solve than manually placed light sources.
Lumen solves indirect specular, or reflections, for the full range of material roughness values.
Diffuse global illumination and shadowed skylight can be seen in all reflections. Lumen Reflections also support Clear Coat materials, like the car example below.
Lumen provides glossy reflections on translucency, like the car windows in the example below.
Lumen Reflections support Single Layer Water materials, with reflections forced to mirror.
The Two-Sided Foliage shading model is solved by gathering lighting from the backface and scattering it through the leaf, attenuated by the material's Subsurface Color.
