I should clarify, it is the emission material that can’t be translucent. It will cast light onto other translucent materials into the scene. It actually may be possible to use translucency with hardware raytracing (I don’t recall and forgot to test, sorry), but this doesn’t work with software raytracing because translucent materials are not included in the mesh distance field representation of the scene.
It can be somewhat noisy/splotchy on small lightsources, especially in diffuse reflections.
5.4.4
Lighting from lightsource actors is computed directly (or more accurate to say, the first bounce is computed directly), rather than through numerical integration. In order to solve the incoming lighting from emissive surfaces, the engine needs to trace rays into the scene and return what it finds. This works, but it’s inefficient and can require a large number of samples which we cannot afford for realtime rendering which is why on small emissive objects the lighting can be unstable.
In a regular offline renderer you would just increase the ray count, but we can’t afford that in realtime, so we’re just sort of stuck with the noise.
I don’t know. As long as Lumen is functioning, the indirect lighting will be shadowed (except for translucent surfaces).
Lightmaps for lighting scenarios can’t be blended together unfortunately. There’s not really a lot you can do about this.
No idea if/when it Nanite will be supported on mobile but my guess is that it’s a long ways off, there’s still a lot of work to be done on feature support and performance for PC platforms.