Abstract: A thin collimated backlight is provided for use in a monochrome liquid crystal display or a color liquid crystal display with color converting elements. The color converting elements are located on the opposite side of the liquid crystal panel to the backlight. The backlight is illuminated by narrow-band light sources such as single color LEDs. The backlight is formed by a lightguide, one or more conventional light controlling sheets and a polymeric filter sheet. The polymeric filter acts to: 1) reflect one polarization direction over the bandwidth of source at all angles of incidence and 2) reflect the orthogonal polarization direction over the bandwidth of the source only at high incident angles. Light in this orthogonal polarization passes through the filter when incident close to the normal to the filter sheet. Light reflected by the filter is efficiently recycled within the backlight.