a plane by definition has no depth, so only one side is rendered meaning only one side can block light. to combat this there is two solutions: give the plane depth (make it into a cube like shape) or set your material to two sided.
a plane by definition has no depth, so only one side is rendered meaning only one side can block light. to combat this there is two solutions: give the plane depth (make it into a cube like shape) or set your material to two sided.