the light source location

CesiumJS
1

How do I get the position of the light source at the specified point in time?

2

So the only light source in Cesium is the sun, and you can get its position using this class:

https://cesiumjs.org/Cesium/Build/Documentation/Simon1994PlanetaryPositions.html

There’s a discussion about adding more light sources, or controlling the light position, which has an example of using that class:

https://github.com/AnalyticalGraphicsInc/cesium/issues/6553

Hope this helps!