Lighting Channels allow dynamic lights to only affect objects when their lighting channels overlap. This is primarily intended for cinematic use to give users powerful control over how Actors are lit. At the moment, Unreal Engine supports up to 3 lighting channels.
Usage
By default, Directional Lights, Spot Lights, Point Lights, and all Actors that can be affected by lights (Static Meshes, Skeletal Meshes, etc.) have Lighting Channel 0 enabled. If you would like a lightable Actor to be affected by another Lighting Channel, you must enable that channel on both the Actor and the light.
Example
In the above image, the white Directional Light can only affect Channel 0, which includes the mannequin on the left and the background Static Meshes, while the purple Point Light can only affect Channel 1, which only includes the mannequin on the right.
You can see how the properties are set here:
Click for full image.
For lights, the property can be found in the Advanced pulldown menu of the Light category in the Details panel. For Actors that can be lit, you can find the Lighting Channels properties in the Lighting category of the Details panel.
Limitations
Lighting channel influence is applied dynamically. This means it won't work with Static Lights or Static Mesh Actors with Static Mobility. Static Mesh Actors with Mobility set to Movable do work, however. You'll need to use either Stationary or Movable lights.
Lighting channels will only affect direct lighting on opaque materials. So, translucent or masked materials will not work.
Performance
The performance impact of using Lighting Channels is minimal, but also non-zero. In a scene with 1 directional light, Radeon 7870, at 1080p for example:
| Lighting Channels Satus | Time in ms |
|---|---|
| off | 0.42ms StandardDeferredLighting 1 draws 1 prims 3 verts |
| on | 0.08ms CopyStencilToLightingChannels 1 draws 1 prims 3 verts |
On Mobile
As of Unreal Engine 4.13, Lighting Channels works on mobile renderers with the following features supported:
- Multiple directional lights are supported in different channels.
- Each primitives can only be affected by one directional, and it will use the directional light from first lighting channel it has set.
- CSM shadows from stationary or movable directional lights cast only on primitives with matching lighting channels.
- Dynamic point lights fully support lighting channels.