Telescopic pixels may brighten low-power displays

A group from Microsoft Research has designed a new display technology that they hope may trounce LCD systems by providing brighter contrast, improved daylight visibility, and decreased energy consumption.

The display is historically one of the biggest energy hogs within a laptop (even though LCDs are very efficient compared with their CRT predecessors), and getting that energy use down without losing image quality has been a fundamental challenge. 

A traditional liquid crystal display consists of a number of pixels lined up in front of a light source, or backlight. In Microsoft’s design, the researchers claim that the backlight can be transmitted through the pixel with 36 percent efficiency, compared to less than 10 percent for LCDs. If they can improve the backlight efficiency to the 56 percent efficiency that the researchers project, battery life in laptops could last about 45 minutes longer, Maximum PC reports. With more backlight passing through, the display can rely on a significantly less powerful light source.

This development – if it makes it out of the lab – could help minimize the environmental impact of consumer electronics.  

To understand their advance, first consider how an LCD works. Each pixel in an LCD consists of polarizing filters layered around two transparent electrodes, made from indium tin oxide, that sandwich molecules of a liquid crystal. The crystals change their shape in predictable ways when they are in the presence of an electric current, and this property can be used to control how much light passes from backlight through the filters. In effect, the liquid crystal acts like a shutter.

One shortcoming of LCD pixels, however, is that they are never fully “off,” meaning that even in their most twisted or unaligned position, some light still escapes through the crystals. They perform very poorly in the presence of ambient light, because only a small percentage of the backlight ever makes it through the filters, making the displays appear dull in bright environments.

Rather than use crystals, the Microsoft Research design consists of two tiny mirrors, which act like a miniature telescope. One of the mirrors, called the primary mirror, changes its shape from flat to curved when a voltage is applied. This curving serves to focus light onto the secondary mirror, which sends the light through a hole onto the display screen. When the pixel is in the off state, the primary mirror is flat, and no light passes through—allowing for a more pure state of black than can be achieved with LCDs.

The researchers expect that essentially the same production techniques used in making LCDs can manufacture telescopic pixel displays, and that the more exotic materials that they currently are working with—that indium tin oxide used in LCDs—could be replaced with extremely thin, nearly transparent layers of aluminum, which is far cheaper to work with and is easier to recycle.

Much more technical detail is available in the original paper, Technology Review’s story, and this Ars Technica breakdown.