Hard to know for sure without being able to compare in that content myself. Here’s a list of differences between Lumen Reflections and RT Reflections:
- By default Lumen Reflections use screen traces, which may help or not. RT reflections didn’t have those.
- RT reflections used reflection captures and unshadowed skylight for things in reflections. This can be enabled in Lumen through CVars. r.Lumen.HardwareRayTracing.LightingMode 3 for unshadowed skylight and.ReflectionCaptures for reflection captures.
- RT reflections exposed whether shadows in reflections should be area or hard. Lumen uses only hard, as those cause less noise. In 5.5/UE5-Main this can be changed using r.Lumen.HardwareRayTracing.HitLighting.ShadowMode
- RT reflections denoiser is sharper. Some of it can be made sharper in Lumen using CVars. Try for example disabling bilateral filter using r.Lumen.Reflections.BilateralFilter 0. There should be new denoiser in 5.5 which will make everything sharper though.