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  • David Kerr thinks this is interesting:

Retinal scanning displays work by drawing a raster image directly onto the retina of the eye, which is the only place where the image actually forms. Users perceive the image as floating in space in front of them. A mobile AR review from 2004 [Höllerer and Feiner 2004] mentions retinal scanning display technology as one of the very few candidates at the time that could produce augmentations with adequate brightness and contrast in direct sunlight outdoors.

From

Cover of Augmented Reality: Principles and Practice

Note

Intel glasses display a monochrome (red) image on the retina.