Lighting environments in Showcase have two lighting components: the image-based lighting (IBL) that is fixed according to the environment you are using, and an environment light that provides directional illumination and shadows.
When you position a highlight of the environment light, the ground shadow is automatically relocated to maintain a realistic lighting effect. In the same manner, highlights change as you move a shadow. You can choose to turn highlights or shadows on or off.
Environment light can cast shadows on the ground and onto objects in the scene. Additional lights in the scene only cast shadows in Ray Tracing mode.