Use light rendering layers

The High Definition Render Pipeline (HDRP) allows you to use Rendering Layers, which are LayerMasks to make Lights or effects only affect specific Renderers.

A Renderer can support up to 32 rendering layers, but all HDRP effects using Rendering Layers only support the first 16 layers. On the image below, you can see usage of Rendering Layers with Lights to only affect some of the meshes.

Rendering Layers are also supported on decal projectors, and can be sampled from the ShaderGraph to implement custom effects.

Configure Rendering Layers

To create and name Rendering Layers:

  • Open the HDRP Global Settings.
  • Go to the Rendering Layers section.
  • Open the foldout Rendering Layer Names.

To use Rendering Layers with Lights:

  • Open the HDRP Global Settings.
  • In the Frame Settings (Default Values) section, open the Lighting dropdown.
  • Enable Light Layers.
  • Open the HDRP Asset.
  • Go to the Lighting section.
  • Enable Light Layers.

To enable and use Rendering Layers with decal projectors, refer to the Decal Layers Documentation.

To access the Rendering Layer Mask buffer from the ShaderGraph, go to the Lighting section of your Project’s HDRP Asset and enable the Rendering Layer Mask Buffer checkbox. You can then use the HD Sample Buffer node and set RenderingLayerMask as the source buffer to sample the layer mask buffer per pixel.

Use a light's rendering layer mask

After you enable Light Layers, you can then use them to decouple Meshes from certain Lights in your Scene. To do this:

  1. Click on a Light in the Hierarchy or the Scene view to view it in the Inspector.
  2. Enable additional properties in the General section to expose the Rendering Layer Mask property.
  3. Use the Rendering Layer Mask property drop-down to select which Light Layers this Light affects.
  4. Click on a Mesh Renderer or Terrain in the Hierarchy or the Scene view to view it in the Inspector.
  5. Use the Rendering Layer Mask drop-down (See MeshRenderer for GameObjects or OtherSettings for Terrain) to select which Light Layers affect this Mesh Renderer or Terrain. When you enable Light Layers, a Light only affects a Mesh Renderer or Terrain if they both use a matching Light Layer.

Use a light's shadow layers

When using Light Layers, Meshes only cast shadows for Lights on the same Rendering Layer as them. This is because HDRP synchronizes Light Rendering Layers and shadow Rendering Layers by default, so every Mesh that receives light, also casts shadows for it. To make a Mesh cast shadows without the Light also affecting its lighting, you must decouple the shadow Rendering Layers from that Light's Rendering Layers.

To do this:

  1. Click on a Light in the Hierarchy or the Scene view to view it in the Inspector.
  2. Go to the Shadows section and enable the Custom Shadow Layers checkbox.

You can now use the Shadow Layers drop-down in the Shadows section to set the Rendering Layers that the Light uses for shadowing. You can also still use the Rendering Layer Mask drop-down in the General section to set the Rendering Layers that the Light uses for lighting.

Rename a rendering layers

By default, in the UI for Lights, Decals, Mesh Renderers or Terrain, Rendering Layers are named Layer 0-15. To more easily differentiate between them, you can give each Layer a specific name. To do this, open the HDRP Global Settings, and go to Rendering Layer Names. Here you can set the name of each Light Layer individually.

Example scenario for Light Layers

Using cookies for light fixtures can sometimes have a negative visual effect on a bulb, such as self-shadowing or transmission contribution. You can use Light Layers to make a bulb Mesh not receive any light from the Light’s cookie, and instead receive light from a separate small Point Light.

The Light cookie incorrectly affects the transmission of this bulb’s geometry.

Assigning the bulb’s Mesh Renderer to a specific Rendering Layer means that the Light cookie no longer affects the bulb’s Mesh Renderer.

To restore the transmission effect, create a Point Light and assign it to the same Rendering Layer as the bulb’s Mesh Renderer. Now this Point Light only affects the bulb’s Mesh Renderer and does not contribute to the rest of the Scene Lighting.

For more information on this process, see Pierre Donzallaz’s expert guide on creating high quality light fixtures in Unity.