Mode-switchable backlight, privacy display, and method

A mode-switchable privacy display comprising:

• a first directional backlight configured to provide narrow-angle emitted light during both a privacy mode and a public mode;
• a second directional backlight configured to provide bidirectional emitted light exclusively during the public mode, the bidirectional emitted light having a bifurcated angular extent that is complementary to an angular range of the narrow-angle emitted light;
• and
• an array of light valves configured to modulate the narrow-angle emitted light as a private displayed image during the privacy mode and to modulate broad-angle emitted light as a public displayed image during the public mode,
• wherein the broad-angle emitted light comprises a combination of the narrow-angle emitted light and the bidirectional emitted light during the public mode.

A method of mode-switchable backlight operation, the method comprising:

• emitting narrow-angle emitted light during both a first mode and a second mode using a first directional backlight to illuminate a first view zone;
• emitting bidirectional emitted light exclusively during the second mode using a second directional backlight, the bidirectional emitted light having a bifurcated angular extent that is complementary to an angular range of the narrow-angle emitted light;
• and
• combining the narrow-angle emitted light and the bidirectional emitted light during the second mode to provide broad-angle emitted light,
• wherein the broad-angle emitted light illuminates a second view zone that includes the first view zone.