5.6.1 - Lumen hardware raytracing "hit lighting" doesn't respect lighting channels

Development Rendering
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1

Exactly as the title says, Lumen hardware raytracing “hit lighting” doesn’t respect lighting channels. See the provided repro project.

I’m not sure if this was the case in 5.5.x, perhaps RT simply ignored non-channel-zero lights, but we didn’t notice it previously one way or another. It’s very obvious now in 5.6.1 if you have a bright light on a non-zero channel.

2

Steps to Reproduce

  • Enabled lumen hardware raytracing (disabling reflection screen traces makes it more obvious, but is not required)
  • Set lumen “Ray Lighting Mode” to Hit Lighting or Hit Lighting for Reflections
  • Create a directional light set to lighting channel 1 or 2
  • Create some meshes that are only using lighting channel 0
    • For “Hit Lighting for Reflections”, add a reflective/mirror-like surface so you can see the other meshes in the reflection
  • Note that the channel 0 meshes in the reflection/GI appear to be illuminated by the channel 1/2 light whereas the rasterized pass does not illuminate the channel 0 meshes by the channel 1/2 light
3

Hello,

Lumen doesn’t support light channels in hit lighting. This is a known limitation, but I’ve created an internal ticket for tracking here Unreal Engine Issues and Bug Tracker (UE\-357552)

4

I see. That’s unfortunate, but I appreciate the quick response.