Starlight (Forge) rewrites Minecraft's light engine to fix lighting performance and lighting errors. It was built for large dedicated servers that suffered from the slow vanilla light engine. This is the Forge version for Minecraft 1.17.1 - 1.20.2.
It only needs to be on one side, server or client. It cannot be used together with Phosphor, and as an invasive rewrite it may break some other mods.
Put it on your Minecraft server with one click from the panel, and players can still join with a vanilla client.