You really want to know about wearable computing. The undisputed leader in the field is Dr. Steve Mann and his EyeTap organization. Check out www.eyetap.org.
It will blow your mind.
EyeTap is a camera/projector system that intercedes with the light entering the eye by using a double-sided mirror (beam splitter) to divert part of the incoming light stream, which is captured by a CCD and transferred to a processing system. This, in turn, sends out appropriate signals to a AREMAC (camera spelled backwards) which sends out a beam to the opposite side of the double-sided mirror which sends it on into the eye in sync with the original light. So you have what amounts to "virtual light" which could include anything from the unmitigated orginal view to a computer augmented view (perhaps including data, xray, ultraviolet or infrared imaging, CAD images, whatever) to a completely computer generated image that may have nothing to do with what you are currently looking at.
For an expanded conceptualization of "virtual light", read the book of the same title by William Gibson.