How does Cesium customize the light source?

I want to customize the position and orientation of the light source for light analysis, but I can't find an interface to modify the sun's light source. Or light analysis like a flashlight, please tell me how to achieve it, thank you very much.

There’s currently no interface for that yet, but there’s been some discussion of adding a feature like that. Check out the GitHub issue below, which includes a workaround for now to set the time of day to control the sun’s position:

I believe the sunlight color for 3D models is hardcoded into the PBR shader.