The display on an e-reader is probaby the most improtant part. Most e-reader on the market use a new display technology called e-paper (Electronic-Paper). These kind of displays are very easy on the eye and are great if you want to read for a long time. E-Paper displays also require very little power as they only draw power when the image actually changes. If you read the same page for a few minutes, there's no power wasted. Currently almost all e-reader are black-and-white, but in the near future we'll start to see color ones, too.
Almost all e-readers today use E Ink, including the Sony readers, Amazon's Kindle, the B&N Nook and others. E Ink is the e-paper pioneer, and was the first display to actually be available commercially. E Ink is capable of producing thin, ultra-efficient and flexible displays, which are currently monochrome, although they are working on color displays, too. E Ink displays can also be found in mobile phones, watches and lot's of other products. One of the drawbacks of E Ink is the slow refresh rate, altough the displays are constantly improving.
E Ink displays are made from tiny capsules. Each capsule includes two kinds of particles - black and white. Using electricity, we can choose whether the black or the white particles are on top - and thus create a black or white 'pixel'.
SiPix, Mirasol, Bridgestone, Liquavista
E Ink is not the only e-paper display in town. Sevaral companies are working on other technologies, too, including SiPix, Qualcomm (with their Mirasol displays), Bridgestone (yeah, the tire company) and Liquavista. Liquavista's displays, for example, are similar to E Ink but offer faster refresh rates and color, too.
During 2010 we hope to see new e-readers that feature these new kinds of displays. Competition will be great, and this will drive all display makers to produce displays that look better, are more efficient, have color, a faster refresh rate and are probably cheaper, too.
Pixel Qi is a company working on a very interesting display that can be switched between an LCD mode and a e-paper mode. You can have a normal laptop display, and when you want you can turn it into a black-and-white display that looks great in sunlight (it is reflective) - but still draws some power even when the imag edoes not change. The first device using such a Pixel Qi should be the Notion Ink Adam. We'll have to wait for it to be released before we know how good those displays actually are.
Yeah, some e-readers use plain-old LCDs. The most notable one is the upcoming Apple iPad. LCDs look great, but draw a lot of power. Because they are use backlighting, they are difficult to read in the sun. Most people find it difficult to look at LCDs for a long time, too, so it's not a great e-reader display for long reading periods.
OLEDs are emissive organic (carbon based) materials. OLED displays are efficient, very thin, and provide great image quality. OLEDs are starting to appear in mobile phones, PDAs, digital cameras and other gadgets (there are a couple of OLED TV sets on the market, too, but these are rather small and very expensive). OLEDs can actually be made transparent and flexible, and these displays open up a lot of new design possibilities.
Unlike LCDs, OLEDs do not require a backlight, beause they are emissive by nature. While OLEDs are better to look at, and more efficient than LCDs, they are still problematic in sunlight, and are probably not the best choice for an e-reader. But still some companies are considering an OLED e-reader, at least according to the latest rumors.