Tim Hobson

Lighting Channels

New Feature in 4.11
Lighting Channels easily allow you to set the actors in your scene that can only be affected by specific lights using the same overlap channel. This is a powerful feature that can give you even more artistic control over your scene and characters. 
 

Ideal Uses

  • Cinematics for rim lighting on characters
  • Better artistic control over lighting the scene
  • Instances where you only need the character or an object to be lit, but not affected by other lights in the scene

How To Enable

This setting can be found in the Details Panel of Static & Skeletal Meshes along with any Directional, Spot, and Point Light.

By default every mesh and light will use Channel 0.  To adjust these channels the light and mesh being affected need to be set to Movable (dynamic) otherwise the options will be grayed out.

How To Use

​1. Select any Mesh in your scene and set it to Movable
2. In the Details panel enable the lighting channel for Channel 1. This will be in addition to Channel 0 already being set. This will allow the Static mesh to accept any lights using either Channel 0 or Channel 1 only. If a light is using Channel 2 only the light source will not be able to affect the mesh. 
​3. Place a Spot or Point light in the scene within range of your Static Mesh. In the Details panel set the lighting channel to only use Channel 1 and disable Channel 0. This means that this light can only affect actors that have the check box for Channel 1 enabled. If other channels are enabled as well this is OK for the actor.
In this example I have a Spot lights below the statue pointed towards the ceiling. This statue has Lighting Channels 0 and 1 enabled. The Spot lights are only using Channel 1 and the surrounding static meshes are only using Channel 0. Since the surrounding meshes can only accept lights with Channel 0 enabled, this means that only the Statue can receive light from my spot light since it has both Channel 0 and 1 enabled! 
This is the default scene from Sun Temple demo, which is available from the Learn tab in the Epic Games Launcher. 
Point Lights & Statue: The two lights in this scene have been placed and pointed towards the Statue. You'll notice that the lighting is shining on the surrounding static meshes for the columns, statue, and pedestal. This is the default for setting for the assets in the scene. The lights here have not yet been set to use specific Lighting Channels yet and are only using Channel 0 which is default. 
Point Lights: The point lights here are using only Channel 1 and have disabled Channel 0. Since the other Static Meshes in the scene will use only Channel 0 by default this means that the lighting from these two point lights can only affect any mesh that is overlapping in the channel values, like the statue.
Statue: The lighting channels here are set to use Channel 0 & 1. This will allow the default lighting from the scene using Channel 0 and the Point Lights using Channel 1 to affect this particular mesh since it's overlapping in the channels used.  

Example Setup

The example below shows the lighting channels being disabled and re-enabled for the floor mesh which accepts all 3 light channels from the Red, Green, and Blue Lights. You will notice that since we are only adjusting the floor, the Cube, Cone, and Sphere are unaffected leaving only their lights lighting them with their own specific channel.

Notes and Workarounds

There may be instances where you want to use Lighting Channels for your static mesh but do not want to have it be a Movable object so that it can be lit by other static lights in your scene. In a situation like this you can temporarily change the Static mesh to Movable and set the lighting channels you want to accept and then reset the static mesh back to Static. You may think that this seems odd since the static mesh is supposed to be movable to accept different lighting channels. This is true, BUT since we plan to use static lighting for this object, but may want to only have it affected by a specific channel light, we can get around the movable issue since the Movable light is the only thing that is absolutely required in order to use Lighting Channels. 

Here is an example if that wasn't confusing enough, right?! 

On the Left, this is a static mesh that has baked lighting for the scene. It was changed temporarily to Movable to set it's light channel and changed back. This static mesh is using both Channel 0 and 1.

On the Right, there is a movable point light that has been enabled for only Channel 1. Since this light is Movable it can adhere to its specified lighting channel and still work with a static mesh that is set to Static.

Limitations

  • This is a SM5 (DX11/Metal) feature only!
  • Only supports setting Lighting Channels for Movable Actors and Lights so it does NOT support Static Lights.
  • Only access to 3 Lighting Channels
  • Skylight actor does not have Lighting Channels
  • Can only affect Opaque Materials