Patent ID: 7841730

Claim:
The light source comprising: a sidelight type backlight light guide plate (L), a transmittance angle dependent polarizing layer (T 2 ) which transmits a polarized light component of one direction of polarization in normal incident light, and selectively reflects the other polarized light component and reflects obliquely incident light regardless of a direction of polarization is disposed on one surface of the sidelight type backlight light guide plate (L), said transmittance angle dependent polarizing layer (T 2 ) is a polarizing element (A) in which a retardation layer (b) is inserted between at least two reflection polarizers (a) having wavelength bands, overlapped one on the other, of selective reflection of polarized light, and a reflection plate (R) having a repetitive slope structure is disposed on the other surface of the sidelight type backlight light guide plate (L), wherein the reflection polarizer (a) is a circular polarization type reflection polarizer (a 1 ) transmitting circularly polarized light, while selectively reflecting reverse circularly polarized light, and the retardation layer (b) comprises a layer (b 1 ) having a front retardation (in the normal direction) of almost zero and a retardation of λ/8 or more relative to incident light incoming at a direction inclined from the normal direction by 30° or more.