Although projectors are widely used in schools and for presentations to large audiences, price has been the major factor in their adoption rather than the size, the power consumption, or, to some extent, the brightness of these projectors. In contrast, size, power consumption, and brightness are the dominant technical specifications that inhibit the incorporation of projectors in handheld devices of various types. The market for such battery-powered “personal projectors” is expected to be much larger than that for “traditional” mains-powered projectors.28
Currently, three major technologies are used to project images that are created or transmitted electronically: digital light processors (DLPs), which use an array of micromirrors to create an image by the reflection of light illuminating the mirrors; liquid crystal on silicon (LCoS), which creates an image by modulating the intensity of the light by means of liquid crystals; and beam steering of one or more lasers, which is used to “write” an image directly on a screen. All three are candidates for future development for incorporation in handheld devices. Such devices have strict requirements on energy consumption, as well as size.
Each of those technologies has advantages and disadvantages, and there is no clear overall winner yet. DLP projectors incorporating RGB LEDs have high image quality and low power consumption, but they have lower resolution than LCoS projectors. Laser scanning also has low power consumption, but laser speckle noise affects image quality. In all cases, the challenge is to provide an image that is large enough to be advantageous over a handheld device’s built-in screen and that is bright enough to be seen under less than ideal lighting conditions and is of a quality that end users consider acceptable and to provide this capability without unacceptable battery drain.
A display can sometimes create the illusion of being three-dimensional when a stereoscopic technology is used to produce images. The human visual system, however, experiences a two-dimensional plane, and it is not true three-dimensional images that are being displayed. In contrast, modern holographic displays are able to produce true three-dimensional images (or holograms) that do not require any
28 The technology for storing images has completely outpaced the technology of the projectors needed to display them. A carousel holding 140 35-mm slides is comparable in volume to that of the projector. Similarly, 140 plastic foils are comparable in volume to that of a portable overhead projector. In contrast, today it is possible to carry more than 10,000 high-resolution images on a tiny flash drive. This capability is driving the desire to create portable projectors, comparable in size to a cell phone, that are capable of displaying these electronically stored images.