Let’s say you just want the noise to go away without having to redo your materials. An easy solution is to simply clamp your materials to a value that won’t generate glossy reflections to begin with. This will not affect direct lighting’s material response, but your reflections will definitely look different. You can use r.Lumen.Reflections.MaxRoughnessToTrace (default .4) to determine the roughest material value lumen will trace reflections for, and r.Lumen.Reflections.SmoothBias (default 0), which will nudge any reflection-receiving surfaces towards being more specular, thus potentially reducing noise.
r.Lumen.Reflections.MaxRoughnessToTrace at .4 (default)
r.Lumen.Reflections.MaxRoughnessToTrace at .3. Note the changed appearance of the floor. What isn’t visible is a new fizzle in the emissive GI on the right of the image.
r.Lumen.Reflections.SmoothBias at 0 (default).
r.Lumen.Reflections.SmoothBias at 1. Note how much shinier not only the floor is, but the adjacent walls and other surfaces.
Both of these CVars can cause visual errors, with the maxroughnesstotrace sometimes revealing lumen GI errors that the reflections hid, or the smoothbias altering the look of rough surfaces too severely. These aren’t magic bullets, but good tools in the toolbox.
It should also be said about the SciFI test scene: this is one of the worst scenes you could support under lumen. It runs the gamut of all potential roughness values, it has very shiny metallic surfaces that require very accurate reflections, and small, irregularly-shaped emissive panels that must propagate lighting. A vast number of modern game scenes, especially those with more diffuse lighting, will resolve better with lumen than this scene will.