Critical Lumen Instability in UE5.6: Artistic Control Severely Impacted

Development Rendering
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Hi,

In 5.6 there were a few changes, which could be responsible for those changes:

  • Indirect lighting intensity and diffuse color boost now also affect hit-lighting. People were complaining that when enabling full hit-lighting those controls didn’t do anything, so we fixed that. But if you used hit-lighting only for reflections then those controls only affected GI. I think we need to fix this and makes those controls only affect non reflection rays, so that it works in a more expected way
  • We tweaked a bit diffuse color boost equation, so that it now leaves value/saturation intact and only boosts luminance. As otherwise all boosted materials were just becoming white
  • Shifted cached lighting range, so that it’s possible now to use realistic lighting values without clamping indirect lighting (loosing indirect bounce). Range was now shifted, so that you can use [-4;24] EV exposure values. You can set it back to previous state by using r.Lumen.CachedLightingPreExposure 0 and r.SkyLight.RealTimeReflectionCapture.PreExposure 0

With default indirect lighting intensity, diffuse color boost and those CVars set to 0 I expect that 5.6 will generate the same image as 5.5 here.

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