The most efficient possible display technology would be something that bypasses the eyes altogether and sends information straight to the brain. Sadly, cranial USB ports are still pretty hard to install. The second most efficient possible display technology anyone's devised projects images directly into the eye. The dream of a wearable virtual retinal display, or VRD, has been around for nearly two decades; it's on the horizon, but it's still going to be a while until it gets here.

The idea of VRD was first tossed around at the University of Washington's Human Interface Technology Lab back around 1991. Thomas Furness, who'd been working on helmet-based displays for the Air Force in the '80s, and research engineer Joel Kollin were part of the team that put together the initial (and enormous) prototype. The concept was that tiny, ultra-low-power lasers could paint an image onto the human retina by scanning across it at high speed,