Large Gamut Backlight for an LCD With Four Primaries

A small backlight unit having four LEDs of different colors is designed and fabricated. Traditionally, the backlight units are lit by white cold cathode fluorescent lamps or by white LEDs. Our backlight unit utilizes four monochromatic LEDs. LEDs are located at corners of the light guide. Outcoupling is accomplished using large period blazed-gratings. The master plate for the light guide is fabricated by laser lithography. The final lightguide is UV-casted on a PMMA plate using an electroplated nickel tool. Proposed backlight unit enlarges significantly the gamut of LCD, if the color filters of the LCD panel have been chosen appropriately. The brightness uniformity and the white balance of the backlight are analyzed by a fiber spectrometer. The brightness uniformity of the backlight is good, over 85%. White balance of the backlight should be further improved.