This mod moves Minecraft's light engine processing to another thread, "fixing" MC-162253 (underlying performance issue still exists, but does not impact FPS anymore).
MC-123584 is also fixed by simply moving all rendering off the main thread. It is recommended to enable the Forge "alwaysSetupTerrainOffThread" option to avoid rendering issues.
Also included is a fix for opening screenshots using the chat link (vanilla behaviour: freezing the game until image viewer is closed).
Forge version this mod was tested to work with: 31.1.27. Version 31.1.87 is currently incompatible.
Block light in single player worlds is not rendered until the light source receives a block update.
Multiplayer worlds do not have this issue.