Lucis

Lucis changes how light is updated on the server. Instead of handling every block change as its own lighting operation, it collects changes that happen close together into regions, which are small owned areas of chunks processed as one unit. Changes that land in the same region are grouped and sent as a single batch to the runtime light system, and where possible the work runs asynchronously before the resulting light data is published back to the vanilla engine.

The same approach covers chunk lighting during world generation. Lucis computes light in the chunk preparation stage through its own relighting path, which the author describes as useful for spawning very large structures without sharp drops in server ticks per second. The author reports lighting work sped up roughly 8 to 12 times over vanilla and faster than ScalableLux or Starlight, though these figures come from the author's own testing.

Lucis is required on the server, and the client may add it as well. It is released under the GNU Lesser General Public License v3.0 or later, is open source, and has public links for its source code and issue tracker. The first release, 1.0.0 for 1.21.1, was published on 2026-07-10.