A light guide device can provide a backlight for an LCD or a projection display. The light guide device includes a light-input end and an opposing end, opposing left and right sides which join the light-input end and the opposing end, and opposing front and back surfaces which join the light-input end and the opposing end. A birefringent film is provided on the opposing left and right sides of the light guide which switches a polarization of incident light. Incident light is provided at the light-input end having a right-handed circular polarization, in addition to light having a left-handed circular polarization. Light emitted from the front surface passes through a linear polarizer which selectively passes light to allow privacy of viewing by a user. The incident light can be provided at the light-input end using one or more cuboid rods, slab light guides, or discrete light sources.