3d widget component shadow problem

so,here is the thing.I wanna use 3d widget component to create a dark scene ,and i try to use spot light to make the player vision focus on the light area.And i found that 3d widget component does’t cast shadow by spotlight or any other type except directional light.Why?
I also try to put some mesh behind the 3d widget component ,it does’t work as i expected.what should i do can make 3d widget cast shadow by other light types.
here is the same question i found by google