US Patent 9558540 Display instrument and image display method

A head-mounted display device including an image display apparatus configured to display a captured image of a portion of an environment viewable through the head-mounted display device; and a dimmer configured to, while the captured image is displayed, allow a portion of ambient light from the environment to pass through the dimmer. Also, a method of displaying information on a head-mounted display device. The method may include displaying a captured image of a portion of an environment viewable through the display device; and dimming ambient light received through the head-mounted display device from the environment while displaying the captured image.