This guide is an updated version of the following Unity blog post: Spotlight Team Best Practices: Setting up the Lighting Pipeline - Pierre Yves Donzallaz.
First, let’s go through the definitions of several important graphics rendering terms that you will encounter frequently in this article.
These operations are repeated many times a second, depending on the frame rate.
The following flowchart provides a high-level perspective of the entire lighting pipeline in Unity, from the point of view of a content creator.
You start by selecting a render pipeline. Then you decide how the indirect lighting is generated and pick a Global Illumination system accordingly. After you’ve made sure all the global lighting settings are tuned appropriately for your project, you can continue adding Lights, Emissive Surfaces, Reflection ProbesA 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
See in Glossary, 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
See in Glossary, and Light Probe Proxy Volumes (LPPVs). Detailing the usage and features of all these lighting objects is beyond the scope of this article, therefore I encourage you to read the Lighting section of the manual to learn how to utilize them correctly in your projects.
Until early 2018, only one render pipeline was available in Unity; the Built-In Render Pipeline. This render pipeline offers a choice of rendering pathsThe technique that a render pipeline uses to render graphics. Choosing a different rendering path affects how lighting and shading are calculated. Some rendering paths are more suited to different platforms and hardware than others. More info
See in Glossary: forward, and deferred.
In January 2018, Unity unveiled the Scriptable Render Pipeline (SRP), which allows you to customize the rendering loop via C# scripting. This is actually a minor revolution in the realm of game engines: users are finally able to personalize the culling of objects, their drawing, and the post-processing of the frame without having to use a low-level programming language like C++.
Unity currently provides two pre-built SRPs:
A tile is a small 2-dimensional square pixel section of the frame, and a cluster is a 3-dimensional volume inside the camera frustum. Both the tile and cluster rendering techniques rely on the listing of the lights affecting every single tile and cluster, whose lighting can then be computed in one single pass with the corresponding list of known lights. Opaque objects will most likely be shaded using the tile system, whereas transparent ones will rely on the cluster system. The main advantage is faster processing of the lighting and the considerable reduction in bandwidth consumption compared to the Built-In Render Pipeline (deferred), which depends on much slower multi-pass light accumulation.
You can use the following decision chart to quickly find out which render pipeline you should select based on a few critical criteria.
You can download the latest versions of HDRP and URP via the Unity Package Manager (Window > Package Manager). The easiest way to get started with one of these SRPs is to create a new project with the Unity Hub and use one of the corresponding templates.
If you want to set up your project for HDRP, ensure you have the required package installed. Then use the HD Render Pipeline Wizard (Window > Render Pipeline > HD Render Pipeline Wizard) to set up your project in one click.
If you have some rendering knowledge, are familiar with C#, and need to fully tailor the renderer for your Project, you can experiment with the SRP concept to create your own Custom Scriptable Render Pipeline. The Universal Render Pipeline is especially easy to extend, due to its smaller shader library and the ability to inject, remove and swap rendering passes rapidly.
Porting your project’s materials from the Built-In Render Pipeline to HDRP or to URP is relatively easy in Unity, thanks to a 1-click material converter under Edit > Render Pipeline > Upgrade…. Note that it is a non-reversible action. Backing up your project beforehand is highly recommended!
Nevertheless, custom shaders will have to be ported by hand, so transitioning from the Built-In Render Pipeline to HDRP or URP during production might be time-consuming, depending on the number of custom shaders you would have to rewrite.
Additionally, because the HDRP is more physically correct than the Built-In Render Pipeline, especially regarding light attenuation and distribution, you should not expect your project to look identical after switching to HDRP.
Furthermore, HDRP and URP are not cross-compatible, as they do not share the same rendering features. Porting your project from HDRP to URP and vice versa is possible, but it is not a 1-click operation and will require manual rework of the lighting, the materials, and the shaders!
Two of the Global Illumination systems available in Unity are:
Realtime Global Illumination: This system is built on Enlighten, a third-party middleware solution. It enables you to adjust your lighting in real-time if you do a precompute and do not modify GameObjectsThe 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
See in Glossary in your scene with the ContributeGI setting enabled. See the HDRP and URP for compatibility information specific to scriptable render pipelines. Unless otherwise specified, the Built-In Render Pipeline supports all features described in this article.
Baked Global Illumination: When you use this system, Unity bakes lighting data into textures called lightmaps, and into Light Probes and into reflection probes. There are two lightmappers: Enlighten Baked Global Illumination and the Progressive Lightmapper (CPU or GPU). See the HDRP and URP documentation for compatibility information specific to scriptable render pipelines. Unless otherwise specified, the Built-In Render Pipeline supports all features described in this article.
The Progressive Lightmapper calculates indirect lighting values using path tracing. It can prioritize precomputing lighting that affects objects visible to the scene viewAn interactive view into the world you are creating. You use the Scene View to select and position scenery, characters, cameras, lights, and all other types of Game Object. More info
See in Glossary camera. Although only updating lighting for parts of lightmaps increases the overall bake time, it also enables you to more quickly iterate on your lighting design.
No matter which Global Illumination system you use, Unity will only consider objects that are marked as “Contribute GI” during the baking/precomputing of the lighting. Dynamic (i.e. non-static) objects have to rely on the Light Probes you placed throughout the scene to receive indirect lighting.
Because the baking/precomputing of the lighting is a relatively slow process, only large and complex assets with distinct lighting variations, such as concavity and self-shadowing, should be tagged as “Contribute GI”. Smaller and convex meshes that receive homogeneous lighting should not be marked as such, and they should, therefore, receive indirect lighting from the Light Probes which store a simpler approximation of the lighting. Larger dynamic objects can rely on LPPVs, in order to receive better localized indirect lighting. Limiting the number of objects tagged as “Contribute GI” in your scene is absolutely crucial to minimize baking times while maintaining an adequate lighting quality. You can learn more about this optimization process and the importance of Probe lighting in this tutorial.
The Unity Editor and Player allow you to use both Enlighten Realtime Global IlluminationA lighting system by Geomerics used in Unity for lightmapping and for Enlighten Realtime Global Illumination. More info
See in Glossary and baked lighting at the same time.
However, simultaneously enabling these features greatly increases baking time and memory usage at runtime, because they do not use the same data sets. You can expect visual differences between indirect light you have baked and indirect light provided by Enlighten Realtime Global Illumination, regardless of the lightmapper you use for baking. This is because Enlighten Realtime Global Illumination often operates at a significantly different resolution than Unity’s baking backends, and relies on different techniques to simulate indirect lighting.
If you wish to use both Enlighten Realtime Global Illumination and baked lighting at the same time, limit your simultaneous use of both global illumination systems to high-end platforms and/or to projects that have tightly controlled scenes with predictable costs. Only expert users who have a very good understanding of all lighting settings can effectively use this approach. Consequently, picking one of the two global illumination systems is usually a safer strategy for most projects. Using both systems is rarely recommended.
The Mode property of a Light component is a common source of confusion.
It is important to note that the mode of a light is only relevant if the Baked Global Illumination system is enabled. If you do not use any global illumination system or only use Enlighten Realtime Global Illumination system, then all Baked and Mixed lights will behave as though their Mode property was set to Realtime.
The following diagram combines a decision flowchart with a comparison table; it can help you decide which light mode is appropriate every time a new light is added into the scene.
As you can see in the previous diagram, all Mixed Lights in a Scene have specific baked and real-time capabilities, depending on the Lighting Mode that you picked in the Lighting window.
There are three modes to choose from:
Shadowmask Lighting Mode has two quality settings:
When using HDRP’s Shadowmask Lighting Mode, the ShadowmaskA Texture that shares the same UV layout and resolution with its corresponding lightmap. More info
See in Glossary feature is enabled in the HDRP Asset assigned in the Graphics settings; it then has to be activated specifically for your camera(s) via the Frame Settings.
See the HDRP and URP documentation for compatibility information specific to scriptable render pipelines. Unless otherwise specified, the Built-In Render Pipeline supports all features described in this article.
Now that we have introduced the render pipelines and the main lighting features, let’s have a look at a few examples of projects and see which settings could be used to light them. Since every project is unique, you might use slightly different options based on your requirements.
If you rely heavily on the Asset StoreA growing library of free and commercial assets created by Unity and members of the community. Offers a wide variety of assets, from textures, models and animations to whole project examples, tutorials and Editor extensions. More info
See in Glossary to build your prototype, the Built-In Render Pipeline could be the only suitable render pipeline, as most assets found on the Store are not fully compatible with HDRP and URP; nonetheless, asset compatibility will improve over time. If you are building all the assets from the ground up and already have a clear idea of your project’s requirements, then you could pick one of the two SRPs (i.e. URP or HDRP) or even create a custom one.
When you are in the early stage of (pre-)production and need a quick turnaround and maximum flexibility for the lighting, you might prefer a full real-time approach that does not require any precomputation, therefore you might want to turn off both Baked Global Illumination and Enlighten Realtime Global Illumination. To alleviate the lack of proper indirect lighting, you can enable Screen Space Ambient OcclusionA method to approximate how much ambient light (light not coming from a specific direction) can hit a point on a surface.
See in Glossary: it can help ground the object in the scene by offering cheap real-time contact shadows.
If you are targeting mobile devices, URP could be a great candidate to ensure solid performance for your game. It is in many cases possible to customise URP to suit your game’s specific needs, with help from a graphics programmer.
The Built-In Render Pipeline and URP both support Shadowmask Lighting Mode which makes it possible for you to bake shadows for static objects while still enabling dynamic objects to cast real-time shadows. If Shadowmasks are too expensive for your project, you can fall back to the cheapest Subtractive mode. Finally, the forward rendering path is probably the best option if you have a very small number of lights in your level(s), and if you’re targeting older hardware.
If you are aiming for AAA-quality visuals on PC and consoles for your linear first-person shooter, HDRP should be the preferred render pipeline. Again, with the help of graphics programmers, a custom SRP could also be developed.
If your levels contain many real-time shadow casting lights (e.g. destructible light props and moving lights), then using the Baked Global Illumination system with the Baked Indirect mode should ensure you get great looking indirect lighting from the Mixed directional light and the Baked lightsLight components whose Mode property is set to Baked. Unity pre-calculates the illumination from Baked Lights before runtime, and does not include them in any runtime lighting calculations. More info
See in Glossary in static light props. If your levels consist of a larger proportion of fixed shadow casting lights, then an approach with Shadowmasks could be recommended because HDRP offers a great hybrid Shadowmask mode which gives you more control over the blend between real-time and baked shadows.
If you also plan to support the Nintendo Switch, then using URP would be recommended, so that you can support most gaming platforms on the market and not having to go through the potentially tedious process of porting your project from HDRP to URP, or vice versa.
If you plan to release a battle royale game for PC and consoles, that features large-scale environments and fully dynamic lighting, you should select HDRP, or extend it to tailor the rendering pipeline to your project. You could consider URP if you are not aiming for AAA visual fidelity and are targeting mobile devices or systems with lower specifications.
For this particular scenario, if you are using the Built-in Render Pipeline, activating both the Enlighten Realtime Global Illumination and a Baked Global Illumination system is not recommended, because the resulting overhead in terms of performance and scene management for an immense level could be problematic. Another argument against the use of both global illumination systems is the unpredictable nature of such large-scale multiplayer games: performance estimations are for instance more difficult than in a highly-scripted linear level.
The rendering landscape has changed radically in Unity over the past few years, thanks to the introduction of the Scriptable Render Pipelines. Therefore, keeping up with all these changes and their implications for the lighting pipeline can be exhausting.
Hopefully, this guide and its many illustrations have given you a better understanding of the capabilities of each Render Pipeline so that you can confidently start your projects in Unity with the appropriate rendering and lighting settings!
You can learn more about the lighting in Unity and the rendering pipelines with the following pages: