Edit: Fixed a bug that causes all lights to lose their first bounce (second and later on is preserved). The binary and GitHub repository are updated.
Binaries, replace Engine/Binaries/Win64/UnrealLightmass.exe directly:
Hint: This mod can be used together with a modified BaseLightmass.ini to get a better result. (especially the CachedIrradiancePhotonDownsampleFactor parameter, default is 2, highest is 1. If you have troubles with small features of the lighting, you can set it to 1, together with a smaller Static Lighting Level Scale)
Single bounce vs 10 bounces:
Brighter in deep space:
Much better color bleeding effect: (Colors are also more vivid)
Removes overdarken corners:
Helps to wash out artifacts:
RealisticRendering demo, single bounce vs 7 bounces:
Lit by a single skylight:
With sun (a directional light) and other spot lights:
This feature is implemented with a radiosity-like technique. The drawback is that the time of “Caching Irradiance Photons” (orange bars in SwarmAgent) will scale linearly with bounce number.
However, this technique allows even the deepest object to get a solid bounce, which is what we want from a multi-bounced sky light:
My own test shows that 5~10 bounces can get very nice results, so it may not be a good idea to raise the bounce number to some crazy things like 50 or 100.