smoothLight

When a light source is broken, its light fades out over a few ticks instead of vanishing at once, and placing one ramps the light up the same way. Covering a light opening with a solid block dims the area gradually, and opening a passage next to a light source lets light flow in smoothly. Without the mod, the game applies a lighting change in one frame, which is what this mod softens.

The mod tracks each position's transitions in the light engine, stepping light emission and opacity toward their target values over several ticks on both the client and the server. Light sources are picked up automatically, including modded ones, and any block that emits light receives the same transitions. The final lighting always matches what vanilla produces once a transition settles, so the end state does not change.

Installation is optional on either side: the mod runs in singleplayer and on servers, and either side can run it without the other. It is published for Fabric, Forge and NeoForge, with files for 1.20.1 and 1.21.1, and the code is open source under the CC0 1.0 Universal license, which places no restrictions on use.