Lighting channels do not function when the number of lights affecting actors is 79 or higher. Any number of lights that is 78 or fewer will honor lighting channel assignments.

Steps to Reproduce
  1. Open attached sample project
  2. Open 'LightChannelIssue' level
  3. Observe 'Floor' StaticMeshActor is set to Lighting Channel 0, Sphere is set to Lighting Channels 1 and 2, and 'BP_SpawnPointLight' is set to Lighting Channel 1.
    Result: 'Floor' is being lit by the 79 point lights even though they are assigned to different Lighting Channels
    Expected: 'Floor' remains unlit

Next, select the 'BP_SpawnPointLight' actor in the level and in the Details tab, adjust the Default > Count value from 79 to any number less than 79 and note that the 'Floor' is no longer being lit by 'BP_SpawnPointLight'.

Now, select the Sphere and uncheck Lighting Channels 1 and 2 (so it is no longer assigned to any Lighting Channel), observe Sphere goes dark.
Select 'BP_SpawnPointLight' again and change the 'Count' value back to 79 or higher, observe that the Sphere lights back up in spite of not being assigned to a Lighting Channel.

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Affects Versions4.
Target Fix4.20
Fix Commit3851889
Main Commit4042226
Release Commit4095966
CreatedOct 20, 2017
ResolvedJan 23, 2018
UpdatedMay 31, 2018