This is more a comment than anything else, but I am very excited to test out lumen and the lighting systems in general come 5.4. It seems like there has been a ton of optimization work, ranging from the broader work of thread parallelization and bindless resource support, down to more specific features like GPU instance culling for RT and the new light grid system, and new features like RT translucent shadows, SampledDirectLighting, and more. I don’t know what the actual performance delta might be 5.3-5.4, but I’m very excited to find out.
Few other features I remembered: lumen now supports translucent objects in reflections, true refraction and multiple refraction events, subsurface profile working in lumen hit lighting, better support of volumetric lighting, and better perf overviews.
If there’s anyone migrating from an offline DCC to UE, they’re going to find that lumen is competitive to an offline renderer in almost every use case, assuming use of the MRQ and cinematic settings.