Yes.
There are a lot of them, the simplest to control is just increasing the Final Gather quality in the post process volume, and/or increasing the Global Illumination scalability to Cinematic. The quality can still be pushed further but you’ll need to do it by console variables. You can read all about this here: Lumen Performance Guide for Unreal Engine | Unreal Engine 5.4 Documentation | Epic Developer Community
A lot of it can only really be learned by looking at the engine code. Epic operates from the philosophy that the code is the documentation. That being said you can get a relatively high level view of how Lumen works based on the technical docs and the teams presentations at Siggraph and beyond:
This PDF is probably the most comprehensive summary of how it works:
Technical docs; much less detailed but more digestible:
Another Siggraph presentation about Lumen’s final gather:
Epic’s Livestream Presentation and Q&A about Lumen:
