Abstract: A flat light source with U-shaped configuration is proposed which can provide substantially uniform surface illumination. The flat light source includes a first transparent portion for use for illumination which may be composed of a first substantially flat light transmission means, a second transparent portion for use as bypass light guide which may be composed of a second substantially flat light transmission means, and a light coupling portion for use as light coupling between said first and second transparent portions, which may have at least one optical prism. The first and second transparent portions which may be positioned substantially parallel each other form a first and second substantially linear cross sections of a substantially U-shaped configuration. The light coupling portion which is positioned near a bottom between said first and second transparent portions forms a substantially bent (or non-linear) cross section of the U-shaped configuration.

Abstract: A flat light source i.e. a surface light source and a passive display using the same are disclosed, capable of making optimal light leakage with uniform brightness across the entire area of its large flat surface. The flat light source comprises a first light transmission means for illumination with relatively high refractive index, a second light transmission means for bypass light guide including at least one light guide having relatively high refractive index and a light coupling means making light coupling between the both first and light transmission means for changing direction of light rays, wherein the light rays output from the second light transmission means are changed in direction in order to input into the first light transmission means.

Abstract: Flat panel light source device comprises first and second light transmission panels and light coupling device. Both panels may have relatively high refractive index and relatively high light transmission characteristics. The first panel is used for illumination and the second panel is used for bypass light guide. Both panels are located adjacently in parallel. The light coupling device makes light coupling between both panels and is located near one pair of side terminals in both panels, distant from another pair of side terminals to which incident light rays are input. The second panel may have at least one of light reflective layer of light transmission material with lower refractive index than the second panel. Alternatively, the second panel may have multiple of optical fibers. A passive type display device comprises a flat panel type passive display device and the flat panel light source in described above. The liquid crystal display device may be used for the passive display device.