An illumination system for a flat panel display device includes: a light guide plate made of an optically isotropic material; a light source disposed at a side of the light guide plate; an upper layer disposed on a top surface of the light guide plate and made of an optically anisotropic material; and a polarization selection emitting structure which is disposed at an interface of the light guide plate and the upper layer. The upper layer has two different refractive indices and one of the two refractive indices is the same as a refractive index of the light guide plate. In the polarization selection emitting structure differently polarized light is differently refracted, reflected, diffracted, or scattered based on polarization direction.