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In order to be useful, handhelds must be thin, light and use as little power as possible. Figuring out how to have crisp, easy-to-read screens incorporated into Windows Mobile devices while simultaneously maintaining these size and power requirements has taken quite a while.
But, in the past few years, real progress has been made. Current Pocket PCs employ two main types of displays that meet all of these requirements and look under any condition: reflective and transreflective (or transflective) TFTs.

Reflective TFTs
Older PDAs, including Palm-size PCs, used transmissive LCDs with backlighting. These screens worked fine indoors in artificial light, but became practically useless outdoors as the sunlight dimmed the screen to black. Reflective TFTs, like those used in the iPAQ 3600 models, overcame this problem. Reflective TFTs cannot be backlit, and so require front lighting. The light from the sun does not wash out these displays, but makes them sharper than ever. Reflective TFTs have the added bonus of not needing powered frontlighting when in the presence of a sufficient light source. Whether it's a well lit hallway or a sunny day, reflective screens can be used and easily read with no self-lighting whatsoever.
原帖地�: TechSpott - Computer and technology forums http://www.techspott.com//showthread.php?p=1023

Transreflective TFTs
Modern Windows Mobile Pocket PCs and Smartphones use transreflective (or transflective) TFTs. These are transmissive (lit from the back) and reflective (lit from the front) and can be lit from front and back simultaneously, making them beautifully viewable indoors and out. These displays have a brighter, crisper look - colors appear more vivid, and black actually looks black. With transreflective TFTs, everything looks better.