Various embodiments may relate to a lens for an illumination device. The lens includes a bottom wall, a top wall, and a circumferential wall. The circumferential wall connects the bottom wall and the top wall. A plurality of regions of the bottom wall respectively arch towards the top wall to define at least one first accommodation cavity having an inner wall as a first incident surface, and at least one second accommodation cavity having an inner wall as a second incident surface. The first and second incident surfaces are designed as different curved surfaces for receiving first incident light and second incident light, respectively. Various embodiments further relate to an illumination device including the lens.