I am very to the unreal engine but I have been messing around a lot in UE5 when I discovered some annoying bug with emissive lighting.
So basically, I was messing around with emissive lighting in UE5, when I noticed that emissive lighting leaves weird lighting artifacts for a very short period of time, I cannot remember seeing such artifacts in when I tried UE4 so I decided to make a quick test level, it turns out I was right, the artifacts dose not appear in UE4 the same way as it does in UE5, I also converted the project to UE5 and the artifacts were back. after a lot of tinkering with different settings, I noticed that the artifacts disrepair when I reduced the anti-aliasing quality to normal, so naturally I tried FXAA and Nvidia DLSS, and they both work completely fine.
TLDR: TemporalAA does not interact properly with Emissive lighting in UE5.
just to show what the bug looks like from both UE4 and UE5’s POV
if anyone knows how to fix this without switching to UE4 / using FXAA/DLSS
then I would appreciate it if you can tell me a solution, and thanks for reading