Unreal Engine 4 (UE4) has support for using different Precomputed Lighting Scenarios in levels. This allows a single level to store and display multiple lighting setups, giving you the flexibility of dynamic lighting, but at the fixed cost of pre-computed lighting. Having the ability to change between different Precomputed Lighting Scenarios is of particular importance for Virtual Reality (VR) or Architectural Visualization projects that require high quality renderings with the benefits of fast performance measures. As you read through this reference, you'll learn how to use Precomputed lighting in your UE4 projects.
In the above image; the Directional Light, Sky Light, and Skybox have been placed in a Lighting Scenario level called Day Scenario. The Spotlights for the streetlights have been placed in a different Lighting Scenario level called Night Scenario.
Feature Limitations
While Precomputed Lighting scenarios have a lot of advantages, there are some disadvantages and limitations that you'll need to be aware of while using them. In the following section, we'll go over some of these limitations and how you can avoid (or work around) them.
- Only one Lighting Scenario level should be visible at any time in a game.
- When a Lighting Scenario level is present, Lightmap data from all Sublevels will be placed inside of it so that only the Day Scenario Lightmaps are loaded when it's daytime. As a result, Lightmaps will no longer be streamed by Sublevels.
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Sublevel Lightmap data is stored in the Lighting Scenarios BuiltData package. Registering Reflection Captures from other Sublevels modifies the active lighting scenario's BuiltData. Loading a sublevel twice and only loading a lighting scenario's BuiltData once will produce the following error:
Error: Reflection capture /Game/Environments/Levels/Your_Level_Name.level_name:PersistentLevel.SphereReflectionCapture_1.NewReflectionComponent uploaded twice without reloading its lighting scenario level. The Lighting scenario level must be loaded once for each time the reflection capture is uploaded.
Using Lighting Scenarios
To use Lighting Scenarios in your UE4 projects, you will need to do the following:
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First go to Window > Levels to open up the Levels Manager.
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With the Levels Manager open, right-click on a Sub level in the Levels menu, go to Lighting Scenario, and select the Change to Lighting Scenario option to make the level a Lighting Scenario level.
When a Lighting Scenario level is visible, its Lightmaps will be applied to the world.
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Make sure the Level Streaming method is set to Blueprint by right-clicking on the Sublevel, going to Change Streaming Method, and selecting Blueprint (if it's not already selected).
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Now place any light or Static Meshes your project needs into either of the lighting levels and then build each level's lighting as you would with any other level.
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Once the lighting has finished building, open up the Persistent Level's Blueprint and then add a Load Stream Level node, connecting it to the Event Begin Play node.
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Connect the Event Begin Play node to the Load Stream Level node and then input the name of the Level you want to load. Also, make sure to check both Make Visible After Load and Should Block on Load to make sure you can see the newly loaded level.
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Press the Play button to launch the project and when the first level loads, it should now be using the Day level lighting. To use Night level lighting, you can use the same setup, but you'll need to change the level name to your night time level (instead of the day time level).
Although there are some notable limitations, using Precomputed Lighting Scenarios in UE4 can provide your project with many benefits; such as improved performance and the ability to change to baked lighting (to meet your project's needs).