How do I add a light source to a .sog file?
.sog file is a file to store gaussian splats, it does not support storage of other objects.
There are some ways to add lights (not real lights, but a simple simulation using a custom shader) as demonstrated here: https://www.reddit.com/r/GaussianSplatting/comments/1lqqrac/new_playcanvas_demo_3dgs_physics_relighting/