Version: 2021.2
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LOD and Enlighten Realtime Global Illumination

Realtime Global Illumination using Enlighten

Unity uses a middleware solution called Enlighten for Realtime Global IlluminationA group of techniques that model both direct and indirect lighting to provide realistic lighting results.
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By default, Realtime LightsLight components whose Mode property is set to Realtime. Unity calculates and updates the lighting of Realtime Lights every frame at runtime. No Realtime Lights are precomputed. More info
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contribute only direct lighting to a SceneA Scene contains the environments and menus of your game. Think of each unique Scene file as a unique level. In each Scene, you place your environments, obstacles, and decorations, essentially designing and building your game in pieces. More info
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. If you enable Realtime Global Illumination (Enlighten Realtime Global Illumination) in your Scene, Realtime Lights also contribute indirect lighting to a Scene.

Render pipeline support

See render pipeline feature comparison for more information about support for Realtime Global Illumination using Enlighten across render pipelinesA series of operations that take the contents of a Scene, and displays them on a screen. Unity lets you choose from pre-built render pipelines, or write your own. More info
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When to use Enlighten Realtime Global Illumination

Enlighten Realtime Global Illumination (Realtime GI) is useful for Lights that change slowly and have a significant visual impact on your Scene, such as the sun moving across the sky, or a slowly pulsating light in a closed corridor. This feature is not intended for special effects or Lights that change quickly, because latency and the number of CPU cycles needed make that sort of application impractical. Enlighten Realtime Global IlluminationA lighting system by Geomerics used in Unity for lightmapping and for Enlighten Realtime Global Illumination. More info
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is suitable for games targeting mid-level to high-end PC systems and consoles. Some high-end mobile devices may also be powerful enough to make use of this feature, but you should keep Scenes small and the resolution for real-time lightmapsA pre-rendered texture that contains the effects of light sources on static objects in the scene. Lightmaps are overlaid on top of scene geometry to create the effect of lighting. More info
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low to ensure acceptable performance.

Using Enlighten Realtime Global Illumination

To enable Enlighten Realtime Global Illumination in your Scene, open the Lighting window (menu: Window > Rendering > Lighting) and enable Realtime Global Illumination.

To disable the effect of Realtime GI on a specific Light, select the Light GameObjectThe fundamental object in Unity scenes, which can represent characters, props, scenery, cameras, waypoints, and more. A GameObject’s functionality is defined by the Components attached to it. More info
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and, in the Light component, set the Indirect Multiplier to 0. This means that the Light doesn’t contribute any indirect light to the Scene.

To disable Realtime GI altogether, open the Lighting window (menu: Window > Rendering > Lighting) and uncheck Realtime Global Illumination.

For detailed step-by-step advice on using Enlighten Realtime Global Illumination, see the Unity tutorial on Precomputed Realtime GI.

How Enlighten Realtime Global Illumination works

Enlighten Realtime Global Illumination splits the Scene into small surface patches and determines the degree to which these patches are visible to each other. At runtime, Enlighten Realtime Global Illumination uses this precomputed visibility information to approximate how Realtime Lights bounce in the Scene, saves the results in a set of lightmaps, and then uses these lightmaps to apply indirect lighting to the Scene. It is computationally intensive to update the lightmaps, and so the process is split across several frames. It takes Enlighten Realtime Global Illumination several frames to propagate changes to indirect lighting throughout the Scene.

Light Probes and Enlighten Realtime Global Illumination

Note that Light ProbesLight probes store information about how light passes through space in your scene. A collection of light probes arranged within a given space can improve lighting on moving objects and static LOD scenery within that space. More info
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behave differently when you enable Enlighten Realtime Global Illumination.

In order to react to runtime changes in Scene lighting, they sample lighting iteratively at runtime.

When you disable Enlighten Realtime Global Illumination in a Scene, Light Probes only use baked lighting data. This means that they don’t react to runtime changes in Scene lighting.

Shadows and Enlighten Realtime Global Illumination

If a Light also casts shadows, Unity renders both dynamic and static GameObjects in the Scene into the Light’s shadow map. The Material Shaders of both static and dynamic GameObjects sample this shadow map so that these GameObjects cast real-time shadows onto each other. The Shadow Distance setting determines the maximum distance at which shadows begin to fade out and disappear entirely, which in turn affects performance and image quality.

Enlighten Realtime Global Illumination results also include soft shadows, unless the Scene is very small. These shadows are typically more coarse-grained than what lightmapping can achieve.

To modify Shadow Distance settings, navigate to Edit > Project Settings > Quality > Shadows.

Performance considerations

Enlighten Realtime Global Illumination uses a set of lightmaps to store real-time indirect bounces. For this reason, enabling it increases memory requirements, even if you are using it along with Baked Global Illumination.

The number of shaderA program that runs on the GPU. More info
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calculations needed to generate lighting also increases when you use Enlighten Realtime Global Illumination because it samples an additional set of lightmaps and Light Probes.

Optimizing Enlighten Realtime Global Illumination

If Enlighten Realtime Global Illumination doesn’t respond quickly enough to changes in your Scene lighting, there are several ways to address this problem:

  • Reduce the real-time lightmap resolution to speed up calculation at runtime.
  • Increase the CPU Usage setting for Realtime GI in the Quality Settings window. The tradeoff is that other systems receive less CPU time to do their work. Whether this is acceptable depends on your Project. This is a per-Scene setting, so you can dedicate more or less CPU time based on the complexity of each individual Scene in your Project.

Disabling the default environment contribution

Unity automatically generates an ambient probe and a default Reflection Probe to ensure that environment lighting affects your scene and the GameObjects in it by default.

To disable the environment contribution in the lighting result for a scene or GameObject that does not have manually created light maps and Light Probes, disable the default Reflection ProbeA rendering component that captures a spherical view of its surroundings in all directions, rather like a camera. The captured image is then stored as a Cubemap that can be used by objects with reflective materials. More info
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and the ambient probe. For more information, see Disabling the SkyManager.

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LOD and Enlighten Realtime Global Illumination
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