Lumen uses a fully dynamic indirect lighting pipeline, which means that the scene geometry, material, and light properties can change at any time. Because of that, Lumen greatly improves artists’ workflow. Not only does this mean lighting updates instantly, but it also removes the wait for build times to get to final lighting quality. In addition to that, Lumen-lit scenes need no reflection cubemaps, since Lumen fully replaces other methods and is able to render geometrically precise reflections.In this video, Paulo Souza, Epic Games Evangelist for Latin America and Brazil, takes you through all of Lumen’s features and provides a high-level overview of how it works. He will also show tips on how to improve lighting and reflection quality, along with some of the best practices to make your Unreal Engine 5 scenes shine.
Source: Unreal Engine Blog