US Patent 8982471 HMD image source as dual-purpose projector/near-eye display

A wearable computing system may include a head-mounted display (HMD) and an optical system with a display panel configured to generate images. The optical system may include an optical element that is adjustable between at least a first configuration and a second configuration. When the optical element is in the first configuration, the images generated by the display panel are viewable at an internal viewing location. When the optical element is in the second configuration, the images generated by the display panel are projected externally from the HMD. For example, the location, refractive index, reflectance, opacity, and/or polarization of the optical element could be adjusted.