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Lighting Best Practices

Tutorial

Advanced

+10 XP

40 Mins

(178)

Summary

Optimizing Scene lighting is not an exact science - your process usually depends on your artistic direction. For this reason, this document provides many different approaches, rather than one recommended workflow. 

Select your Unity version

Last updated: May 02, 2023

2018.1

Language

English

1.Lighting Scenes

Optimizing Scene lighting is not an exact science - your process usually depends on your artistic direction. There are many parts to creating a pleasing ambiance, and it can depend heavily on the project and its unique architecture, including whether the project uses single Scenes, Multi-Scene editing, or additive loading. For this reason, this document provides many different approaches, rather than one recommended workflow. The following sections, in particular, contain good advice on this subject:
Auto Generate and Generate Lighting
Lighting Settings
Multi-Scene editing
When you start a new project, apply the following settings to use multiple Scenes correctly and achieve a smooth lighting workflow:
Enable Auto Generate only with single Scenes (see the next section, Auto Generate and Generate Lighting ).
Do not mix Scenes with Auto Generate enabled and Scenes that have Auto Generate disabled.
Whether using Multi-Scene editing or additive loading, ensure that all Scenes used together have identical Lighting Settings, with a focus on Global Settings.
If you are interested in making great visuals in Unity, see the Making believable visuals in Unity best practice guide.

2.Auto Generate and Generate Lighting

Auto Generate
Unity enables Auto Generate by default in all new Scenes. To disable Auto Generate, go to the Lighting Settings (menu: Window > Lighting > Settings) window, scroll down and uncheck the Auto Generate checkbox.
When you enable Auto Generate and a Scene makes use of Baked Global Illumination (GI) or Precomputed Realtime GI, Unity rebuilds the lighting data as you edit the Scene. This means that the backend runs every time the elements in the Scene are changed in a way that affects the baked data; for example, deleting a static GameObject from the Scene triggers a bake.
You should enable Auto Generate only when you are quickly iterating on the lighting while working with a single Scene. In all other cases, you should disable Auto Generate and generate the lighting data manually.
Generate Lighting
Once you disable Auto Generate, you can generate lighting data by clicking the Generate Lighting button. This button can be found in the Lighting Settings window, next to the Auto Generate checkbox.
Lighting Data Asset
When you click the Generate Lighting button, Unity creates a Lighting Data Asset in the Project. This Lighting Data Asset contains the Scene's GI data, along with supporting data Unity uses to create the lighting for the Scene. The Lighting Data Asset is linked to the Scene.
When you use Auto Generate, Unity does not create a Lighting Data Asset in the Project. Instead, Unity stores the GI data and other lighting data for that Scene in memory. This is for two reasons:
Making changes to data in memory is much quicker than writing data to a file.
Making changes to a Lighting Data Asset flags the Scene the Asset is linked to as dirty, which in turn triggers Unity to reserialize that Scene. Auto Generate is intended to promote fast iteration, so it is important that it does not trigger these resource-intensive operations every time it runs.
Testing Scenes with Auto-Generated Lighting Data in Play Mode
The lack of a Lighting Data Asset on disk can lead to problems when testing Scenes in Play Mode. Put simply, Scenes with auto-generated lighting data only appear with all of their correct GI data in Play Mode is in the following scenarios:
Scenario 1:
A Scene is open for single-Scene editing in Edit Mode
You immediately transition from editing only that Scene in Edit Mode into testing only that Scene in Play Mode
Scenario 2:
A collection of Scenes are open for multi-Scene editing in Edit Mode
You immediately transition from editing that set of Scenes in Edit Mode to testing that set of Scenes in Play Mode
Any other set of circumstances cause Scenes that use auto-generated lighting data to appear noticeably wrong in Play Mode. Direct and Realtime lighting (for example, the Skybox or Ambient Source data) continue to function, but GI effects are missing.
Problems with Auto-Generated Lighting Data in Play Mode
Unloading Scenes in Play Mode
When you test a single Scene or collection of Scenes with auto-generated lighting data in Play Mode as above, Unity loses the GI data for those Scenes when those Scenes are unloaded.
This is because when Unity enters Play Mode for a Scene with auto-generated lighting, it attaches GI data directly to the GameObjects in that Scene. When Unity unloads the Scene, it destroys the GI data along with the GameObjects. Because there is no Lighting Data Asset on disk for Unity to reload the GI data from, Unity cannot recover this data without returning to Edit Mode. This means that if Unity loads the same Scene or Scenes again within the same Play Mode session, the Scene or Scenes appear without GI.
Loading additional Scenes in Play Mode
When you open a single Scene and enable Auto Generate in Edit Mode, Unity loads GI data for that Scene from its GI cache (if available) or generates new GI data for that Scene. This GI data resides in memory along with the other lighting data required for the Scene, and is correctly associated with the Scene when you enter Play Mode.
When Unity loads a Scene baked with Auto Generate using a user script in Play Mode, its GI data isn't resident in memory. If you load the Scene non-additively, this appears obviously wrong. If you load the Scene additively, the effects may be more subtle and the cause may not be initially obvious.
Multi-Scene Editing
When multiple Scenes are open for editing with Auto Generate enabled, Unity stores the lighting data for this specific combination of Scenes in memory.
As long as you only want to test this specific combination of Scenes (by immediately entering Play Mode), you can use this as a way to quickly iterate on the lighting for these Scenes. When you enter Play Mode with the Scenes open, Unity does not need to load any state from disk as all the Scene elements already have their GI data attached.
However, if you want to test a different combination of Scenes in Play Mode, or to load these same Scenes but in a different manner (for example, by loading Scene A first and then additively loading Scene B and Scene C), you will experience problems. Any Scenes with auto-generated lighting that you do not open immediately in Play Mode will not have GI data.

3.Lighting Settings

The Lighting Window (menu: Window > Lighting > Settings) contains various options that control the appearance of lighting.
The Scene tab of the Lighting Window allows you to apply lighting options to specific Scenes, rather than to the whole Project. These are known as Scene lighting settings. Unexpected lighting results can occur when Unity has more than one Scene open, and those Scenes have different Scene lighting settings. This can happen when you use Multi-Scene editing in Edit Mode, or when you additively load Scenes in Edit Mode, Play Mode, or a built Project.
When handling multiple Scene lighting settings, Unity is able to combine some settings without problems but must completely overwrite or merge others. Understanding which lighting settings are unaffected, which are overwritten, and which are merged is crucial to lighting multiple Scenes.
Global Settings are settings that Unity merges or overwrites when loading multiple Scenes.
Scene-dependent Settings are settings that are unaffected when Unity loads multiple Scenes.
Global Settings
The following settings are Global:
All settings in the Environment section
Realtime Global Illumination
Mixed Lighting
Lighting mode
Directional Mode
Indirect intensity
Albedo Boost
All settings in the Other Settings section
Auto Generation
Carefully consider these when you use Multi-Scene editing or additive loading. When multiple Scenes are open, and those Scenes have conflicting Global settings, Unity merges or overwrites these settings. This can lead to unexpected lighting results. As such, Scenes that Unity additively loads at the same time in Play mode should use identical Global settings.
When multiple Scenes are open, the Global settings of whichever Scene Unity loads first become the default Global settings. These default Global settings are the base settings for any subsequent additively loaded Scenes, which Unity then adds or merges data. This persists until you set another Scene as active (by destructively loading another Scene or by calling SceneManager.SetActiveScene()). At this point, the active Scene's Global settings become the default.
Any new Scene which Unity loads additively merges its GI data into the existing one. For example, Scene A has a daytime skybox, and Scene B has a night-time skybox. If you load Scene A first, and then additively load Scene B, Unity uses the sunny skybox for both.
Scenarios involving Realtime Global Illumination are particularly complex. To expand on the above example, let's say that Scene A (with the daylight skybox) and Scene B (with the night-time skybox) both use Realtime GI. If you load Scene A first and then additively load Scene B, Scene B incorporates the new environment lighting correctly and appears with daylight conditions. However, if Scene A has Realtime GI disabled, the additive result is a daylight environment with Scene B still showing baked night-time results.
The setting Realtime Global Illumination is a Global Setting as well. If you disable Realtime GIobal Illumination in a Scene, and additively load another Scene that has Realtime GI enabled while it generates its lighting, it only uses the baked results if attainable. Similarly, the effects of Directional mode vanishes when the active Scene does not have Directional mode enabled. Directional mode requires an additional Texture, and dismisses it if the mode is disabled in the active Scene.
Scene-dependent Settings
You can combine specific Lighting Settings appropriately. The following settings are Scene-dependent and do not affect other Scenes after a successful bake:
All settings of the Progressive Lightmapper
Lightmap Resolution
Lightmap Padding
Lightmap Size
Compress Lightmap
Ambient Occlusion
Final Gather
For example, Unity safely combines a Scene baked with a Lightmap Size of 1024 with a Scene baked with a Lightmap Size of 512. This is because the lightmap resolution after the bake is no longer relevant because the result is a texture that the Unity runtime uses. If you want to use lightmaps of different resolutions you may want to examine the Lightmap Switching Tool.
Please note that if more than one Scene is open in the Editor, the Lighting Settings Inspector shows only the settings for the "main" Scene - that is, the Scene that Unity loads first, or whichever one you have subsequently set as the active Scene.

4.Multi-Scene editing

When you work with Multi-Scene editing, please make sure that the Lighting Settings of all individual Scenes match the combined Lighting Settings.
Unity creates one single Lighting Data Asset in the Project even when loading multiple Scenes in the Editor. When loading multiple Scenes, the Lighting Data Asset contains one Lighting Data Asset for each Scene. In the Project window, unfold the combined Lighting Data Asset container to see the single Lighting Data Asset that each Scene references.
Even with Multi-Scene editing, the Editor shows one unified set of Lighting Settings, which is a source of potential confusion. Each Scene retains its settings, and the Editor displays only the result of all Scenes merged. Loading each Scene individually in the Editor or Play Mode might show that they have different settings. Changing the order of loading or making another Scene active in Play Mode or Edit Mode can then suddenly cause a diﬀerent overall appearance.
Note: The Lighting Settings also include the Auto Generation setting. Click the Generate Lighting button to trigger a Multi-Scene bake. Unity only loads the result of this bake if the Scene is the actual driver. If an additionally loaded Scene has Auto Generate enabled in its Lighting Settings, it impacts the GI. Loading this Scene individually or setting the Scene active in Play Mode results in all GI vanishing.

Lighting Best Practices

General Tutorial Discussion

1. Lighting Scenes

2. Auto Generate and Generate Lighting

3. Lighting Settings

4. Multi-Scene editing