Optical element, planar lighting unit and liquid crystal display unit

摘要

An optical element gathers light emitted from a planar luminous element having isotropic light emitting characteristics. The optical element includes an incidence plane and a plurality of protrusions. The incidence plane is formed on one side of the optical element for permitting the light to enter the optical element and faces the planar luminous element. The protrusions are formed on the other side of the optical element and each protrusion has a shape of a frustum.