Such a display would offer the ability to display your speed or distance between other vehicles in real time, superimposing it over the actual road view depicted in the mirror.
The prototype, designed by U.K.-based Light Blue Optics, is far smaller than current vehicular HUD systems and uses constructive and destructive light interference to build the display, reports Technology Review.
The device was presented at the Society for Information Display's Vehicles and Photons 2009 symposium, in Dearborn, Mich.
The benefits of such a device are twofold: First, this broadens the possible implementation of such technology, and second, it can help improve driving safety by overlaying relevant information on top of the actual road view, keeping drivers' eyes where they need to be.
Oh, and as for the holographic part of it? True holograms have nothing to do with it. The projectors use liquid crystal on silicon to modulate beams of red, green, and blue laser light to create an image -- thus using principles of holography (projected image via light interference) without actually creating a hologram.