The present disclosure relates to a lens. The lens includes a bottom surface, a top surface, and a side surface. The top surface is opposite to the bottom surface. The center of the bottom surface is recessed towards the top surface to form a light incident groove. The top surface is recessed towards the bottom surface to form a light-emitting groove. The side surface is connected between the bottom surface and the top surface. The side surface defines a microstructure, and the side surface is fully covered by the microstructure.