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:
https://github.com/AnalyticalGraphicsInc/cesium/issues/6553
I believe the sunlight color for 3D models is hardcoded into the PBR shader.