What is starlight and what does it do? Is it allowed and where can I download it?

Starlight is a performance boosting mod. I think it optimizes the light engine just like phosphor but better and yeah it's allowed for speedrunning. Here is the download link: https://github.com/Tuinity/Starlight/releases/tag/1.0.0-RC2

Starlight makes your loading time shorter, so you spend less time waiting for the world to be created. If you use phosphor currently, you'll have to remove from your mods folder to use starlight. And you'll put starlight in your mods folder :)