Patent ID: 6894814

Claim:
An apparatus comprising: a first group of first, second, and third holographic optical elements electrically switchable between active and inactive states; a second group of first, second, and third holographic optical elements electrically switchable between active and inactive states; wherein each holographic optical element comprises front and back oppositely facing surfaces; wherein each of the first holographic optical elements diffracts first bandwidth light incident on the front surface thereof when operating in the active state, wherein first bandwidth light diffracted by each of the first holographic optical elements emerges from the back surface thereof, and wherein each of the first holographic optical elements transmits first bandwidth light incident on the front surface thereof without substantial alteration when operating in the inactive state, wherein first bandwidth light transmitted by each of the first holographic optical elements emerges from the back surface thereof; wherein each of the second holographic optical elements diffracts second bandwidth light incident on the front surface thereof when operating in the active state, wherein second bandwidth light diffracted by each of the second holographic optical elements emerges from the back surface thereof, and wherein each of the second holographic optical elements transmits second bandwidth light incident on the front surface thereof without substantial alteration when operating in the inactive state, wherein second bandwidth light transmitted by each of the second holographic optical elements emerges from the back surface thereof; wherein each of the third holographic optical elements diffracts third bandwidth light incident on the front surface thereof when operating in the active state, wherein third bandwidth light diffracted by each of the third holographic optical elements emerges from the back surface thereof, and wherein each of the third holographic optical elements transmits third bandwidth light incident on the front surface thereof without substantial alteration when operating in the inactive state, wherein third bandwidth light transmitted by each of the third holographic optical elements emerges from the back surface thereof; a display device configured to display a monochrome image frame; wherein the display device is configured to be illuminated directly or indirectly with light emerging from one of the first, second, or third holographic optical elements while the display device is displaying the monochrome image frame.