A lens includes a light incident surface and a light output surface. The light incident surface includes a first region having points equidistant from the central point of a light emission surface of the light emitting element. The first region satisfies θa≦θ1≦θb, wherein θ1 is a first incident angle of any light emitting from the light emitting element. In a second region with 0° 0.9. In a third region with 0° 0.9. θ2 is a second incident angle of the light of θ1 when traveling in the lens, and θ3 is a third incident angle of the light of θ1 when emitting out of the lens.