1. Field of the Invention
This invention generally relates to electronic displays and, more particularly, to a display capable of selectively operating in wide and narrow display ranges.
2. Description of the Related Art
Large panel liquid crystal (LC) displays normally require large viewing angles, and designs have been significantly improved to expand the viewing angles to near 180°. However, for portable display devices, more limited viewing angles are often desirable in the interest of privacy. To that end, 3M has developed passive films that can be used to cover displays, limiting the viewing angles to about 40°. For example, such a film can be used in airline seat displays to limit images that can be seen by neighboring passengers. However, these films degrade the image quality by placing extra film layers over the LC front panel, and such a display has a limited number of applications.
FIG. 1 is a diagram depicting a display with switchable viewing angles (prior art). One such device is presented by Takatoh et al., “New Peeping Prevention Technology to Control Viewing Angle Properties of TFT-LCDs”, SID Digest, 2006, pp. 1340). When working in the narrow viewing angle mode, people outside the viewing angle can only see checked black and white blocks, thus protecting privacy. However, this method does not limit the backlight spreading angles, so that light emitted outside the narrow viewing angle is wasted, leading to poor display power efficiencies. The waste of energy is particularly critical for hand-held devices with battery supplied power.
It would be advantageous if a display device viewing angle could be switched by controlling the angle at which the backlight panel of the display supplies light to the front panel.