Lumen is a real-time global illumination and reflections system that provides fully dynamic indirect lighting and reflections for your Twinmotion scenes. The Lumen system improves global illumination significantly by simulating with greater accuracy how light interacts with objects and how light and reflections transfer between objects.
This page provides an overview of Lumen in Twinmotion and how it works. For information on how to use Lumen and for best practices to follow for optimal results, refer to Using Lumen Global Illumination.
Lumen Global Illumination in Twinmotion.
Global illumination simulates how light interacts with objects and materials and provides accurate lighting and reflections to your scenes.
The Real time rendering mode in Twinmotion provides global illumination using two methods: Standard and Lumen.
The Standard option approximates global illumination based on Light Propagation Volumes (LPV). This method provides fast results but with less quality and accuracy than Lumen.
The Lumen option is based on ray tracing and accurately simulates indirect lighting by providing diffuse interreflections with infinite bounces and specular reflections (single and multiple).
Diffuse interreflections occur when light directly hits an object that is not shiny or specular, and the light hitting the object bounces onto other nearby surfaces and illuminates them. If the object has a diffuse color, the bounced light takes on this color and illuminates the other nearby surfaces with the same color.
Lumen diffuse interreflections. Specular reflections occur when the light emitted from an object reflects onto a shiny or glossy nearby object, such as a mirror reflection.
Lumen indirect specular reflections.
Lumen Technical Details
Surface Cache and Cards
Lumen captures the material properties for each mesh from multiple angles and generates a Surface Cache with this information. This data is used to quickly find direct and indirect lighting information at ray hit points in the scene. Each of these captured surface positions is called a Card and is generated offline for each mesh.
Lumen Ray Tracing
Lumen is based on ray tracing, a rendering technique that produces high-quality realistic lighting, reflections, and shadow effects. Ray tracing can be software or hardware-based.
Software ray tracing works on a wide range of hardware platforms and operating systems, but has limits as to the types of geometry, materials, and workflows it can use.
Hardware ray tracing supports a larger range of geometry types, materials, and workflows, but requires more powerful system requirements than software ray tracing to operate.
Currently, Twinmotion only supports Lumen in hardware ray tracing mode on Windows, and software ray tracing mode on MacOS.
System Requirements
The system requirements for using Lumen are as follows:
Windows
Operating system: Windows 11 64-bit version, or Windows 10 64-bit version 1909 revision .1350 or higher, or versions 2004 and 20H2 revision .789 or higher.
Render Hardware Interface (RHI): DirectX 12.
Graphics card: NVIDIA RTX-2000 series or higher, or AMD RX-6000 series or higher.
MacOS
Operating system:
Minimum: MacOS 12.5 Monterey.
Recommended: MacOS Ventura 13.
Graphics Processing Unit: Requires a discrete GPU, as opposed to an integrated CPU/GPU.
Graphics card: Metal 1.2 compatible.
Lumen Features
Lumen brings powerful and dynamic global illumination features with real-time performance to Twinmotion.
Lumen Diffuse Indirect Lighting
Lumen global illumination provides dynamic diffuse indirect lighting by continuously bouncing light that hits surfaces onto other nearby surfaces. Although every bounce has a high computational cost and affects render times, this behavior mimics reality, where light bounces indefinitely from one surface to another until the light source loses all energy.
Diffuse indirect lighting produces an effect called color bleeding.
If the initial light source is colored, the bounced light reflects this color onto other surfaces.
If the surfaces have a diffuse color, the bounced light also reflects this color onto other surfaces.
Objects in the scene that block this diffuse indirect lighting produce diffuse indirect shadows.
The scene below shows the diffuse indirect lighting effect created by Lumen global illumination.
Lumen and Ambient Lighting
Lumen improves the quality of ambient lighting and reflections for a more natural effect. This includes the lighting in scenes with sky shadowing where indoor spaces are much darker than outdoor lighting.
Lumen also provides global illumination for translucency and height fog effects, but of lower quality than for opaque surfaces.
In the image below, ambient lighting illuminates the height fog in the scene.
Lumen and Emissive Materials
With Lumen, objects that have materials with emissive properties can bounce specular and diffused light to other nearby objects. For example, you may want to apply a material with emissive properties to a primitive object, such as a cube, and place it in the scene for lighting.
However, noise artifacts can appear in the scene if the cube is too small and bright. Instead of using objects with emissive materials to light a scene, we recommend using placed light sources from the Twinmotion Library.
For more information, refer to Surface Size and Emissive Properties.
In the image below, a sphere with emissive material properties lights the scene. The size of the sphere is large enough for light to bounce correctly without any noise artifacts.
Lumen Reflections
Lumen provides dynamic diffuse and specular reflections on all the Roughness values of materials, from 0% to 100%.
Lumen handles skylight shadows, provides glossy reflections on translucency, and supports multiple specular reflections (the reflection of light between two or more reflective surfaces).
The image below shows how emissive surfaces affect diffuse and specular reflections, and how they are affected by the roughness values of the surrounding surfaces.
Supported Light Types
All light sources and light types in Twinmotion benefit from Lumen global illumination. This includes High Dynamic Range Images (HDRIs), the Twinmotion Dynamic Sky, and the lights in the Twinmotion Library.
Known Issues
Scattered and painted vegetation: Scattered and painted vegetation does not contribute light bounces to Lumen global illumination.
Scattered vegetationManually placed vegetationVR mode: Lumen is supported in Virtual Reality (VR) mode. However, due to the very high hardware requirements you must explicitly allow it by selecting the Enable Lumen in VR checkbox in the VR Quality settings of the Preferences panel. As well, using Lumen in VR mode can introduce rendering artifacts in certain scenes.
Reflections:
Objects that are not visible in the Viewport are not reflected or are reflected at a lower quality.
Translucent materials such as glass and particle sprites do not render properly in surrounding reflections, and do not appear in reflections if they are not visible in the Viewport.
Mirror materials do not reflect the scene as accurately as expected. We do not recommend using objects with mirror materials as focal points in a scene.
