Patent ID: 7492516

Claim:
An optical element, comprising: at least two laminated layers of reflective polarizer; and at least one layer of retardation layer for changing polarization properties laminated between the reflective polarizers, the combination of the layers being designed so as to provide a incident-light transmittance depending on an incident angle of an incident light and designed such that a shielded light is not absorbed but reflected, wherein a first layer of the reflective polarizer is a circular polarization type reflective polarizer capable of transmitting a certain circularly polarized light and selectively reflecting an oppositely circularly polarized light; a second layer of the reflective polarizer is a linear polarization type reflective polarizer capable of transmitting one of perpendicular linearly polarized lights and selectively reflecting the other of the perpendicular linearly polarized lights; and the retardation layer is a layer having a front in a direction normal to the surface of the retardation layer with a retardation value of about λ/4 and having a retardation value of at least λ/8 with respect to an incident light inclined by at least 30° to the normal direction; wherein the retardation layer is a biaxial retardatin layer having an Nz coefficient of at least 2.0, wherein the Nz coefficient is defined by the formula: (nx−ny)/(nx−ny), where nx and ny are each principal in-plane refractive indices, and nz is a principal refractive index in the thickness direction; and the biaxial retardation layer has a slow axis whose direction is set to make an angle of 45°±5° or −45°±5° with a polarization of the linear polarization type reflective polarizer.