Custom directional light using ShadowMaps

I’m new to Cesium.

Looking for a way to model a custom directional lamp. Sun light shall be disabled somehow and the custom lamp shall be lighten instead.

It’s an attempt to visualize antenna’s radio wave propagation.

I use 3D tiles for buildings and a terrain.

Is there a way to model a custom light (lamp) other than the sun light?

If so, I already have tried using ShadowMaps, but I’m not able to direct the light (the shadows) in certain direction.