Sundial Lite is the free and open source version of Sundial, using GNU General Public Licence 3.0. It's designed to make the balance between quality, performance and compatibility.
Optifine released after 04.12.2019 (1.8.9 L5) is supported.
Theoretically can run on Iris 1.5.0 and above, but for less bugs, latest Iris is suggested.
Sundial Lite contains most features from the full version and with some extra features, including but not limits to:
As a compartion to the full version, it does not use voxelization and world space ray tracing, reducing volumetric light and reflection from computing 2 times to 1 time, losing multiple bounce reflection, but have much better performance and mod compatibility.
Mod support > Mod night vision compat can fix it on those versions