High-Luminance Mid-Air Image Display for Outdoor Viewing by Focusing Sunlight

The mid-air image is a very powerful method for presenting computer graphics in a real environment, but it cannot be used in bright locations owing to the decrease in brightness during the imaging process. Therefore, to form a mid-air image with a high-brightness light source, a square pyramidal mirror structure was investigated, and the sunlight concentration was simulated. We simulated the tilt angle and combination angle of the condenser as parameters to calculate the luminance of the surface of a transparent liquid crystal display. The light collector was installed at 55∘ from the horizontal plane and mirror. A high level of illumination was obtained when these were laminated together at an angle of 70∘. To select a suitable diffuser, we prototyped and measured the brightness of the mid-air image with an LED lamp to simulate sunlight in three settings: summer solstice, autumnal equinox, and winter solstice. The maximum luminance of the mid-air image displayed by collecting actual sunlight was estimated to be 998.6 cd/m2. This is considerably higher than the maximum smartphone brightness to allow for outdoor viewing, and it can ensure fully compatible visibility.