https://www.reddit.com/r/unrealengine/comments/1cpmwmg/is_a_lumen_only_game_too_gpu_demanding_for_todays/
r.Lumen.DiffuseIndirect.Allow (0 or 1)
Will stop emissives from casting light onto nearby surfaces, which is insanely expensive. There may be a way to reduce the 'quality' of this, but other than adjusting the temporal blending I couldn't figure it out.
r.Lumen.ProbeHierarchy.SamplePerPixel
r.Lumen.DiffuseIndirect.CullGridPixelSize
r.Lumen.DiffuseIndirect.CardTraceEndDistanceFromCamera
r.Lumen.IrradianceFieldGather.NumProbesToTraceBudget
r.Lumen.DiffuseIndirect.MinTraceDistance
r.Lumen.ScreenProbeGather.RadianceCache.GridResolution
r.Lumen.DiffuseIndirect.Allow
r.Lumen.ScreenProbeGather
r.Lumen.ScreenProbeGather.ScreenTraces
r.Lumen.ScreenProbeGather.Temporal
r.Lumen.ScreenProbeGather.Temporal.MaxFramesAccumulated
r.Lumen.ScreenProbeGather.VisualizeTraces
r.Lumen.ScreenProbeGather.DownsampleFactor
r.Lumen.ScreenProbeGather.ScreenTraces.HZBTraversal.MaxIterations
also volumetrics are actually very cheap at low resolutions
r.VolumetricFog.GridPixelSize
r.VolumetricFog.TemporalReprojection
Shadows also play a huge role
sg.ShadowQuality
r.Shadow.Virtual.Enable
r.ShadowQuality
r.Shadow.MaxResolution
r.Shadow.Virtual.ResolutionLodBiasDirectional=0
As for Lumen, I recently added these cvars to my commonly used list to improve performance:
r.Lumen.ScreenProbeGather.StochasticInterpolation=1 r.Lumen.ScreenProbeGather.SpatialFilterNumPasses=2
- Consider enabling single pass projection, which is experimental but helps a lot with lighting cost
- Set up strict light culling distances
- Disable shadow casting on fill lights
- Use Temporal Upscaling; TSR is the default, TAA in UE5 is now TAAU which also supports upscaling. Set your screen percentage to something like 80% with the option to reduce it on lower end hardware, this is a considerable performance boost but comes at the cost of scene quality