Lighting problems with Cesium loading 3DTiles models

I have come across some tough problems in my work recently, Just as the title describes, I have some 3dtiles data that needs to be loaded into Cesium, But the model in my data is always affected by light and has a difference in brightness.

I have tried many ways to solve this problem, For example, use DirectionalLight to generate a fixed beam of light, But this effect is not what I want.

I also tried generating The 3DTiles without having them use ambient light, The successful! Unfortunately, my team didn't allow me to modify 3dTiles. So, is there a way to make the models in 3DTiles unaffected by time or light.

This is the normal model:

This is at a different Angle:

I want them to be consistent regardless of time or light source.

This is what I did with DirectionalLight:

    viewer.scene.light = new Cesium.DirectionalLight({
      direction: viewer.scene.camera.directionWC,
    });
    viewer.scene.preRender.addEventListener(function (scene, time) {
      viewer.scene.light.direction = Cesium.Cartesian3.clone(
        viewer.scene.camera.directionWC,
        viewer.scene.light.direction
      );
    });