/home/Notoveryet

what is transmissive LCD display…?

Posted in Science, Technology by notoveryet on July 31, 2009

While reading specification of  “BlackBerry Curve 8900” smartphone, we came accross this term – “Transmissive TFT LCD” reading (My friend Amit is planing to buy this phone)…

though I had some idea about this and similar other technology (Reflective TFT LCD), but to know exactly what these technologies are, I did a quick googiling… and here it is for reference…. 🙂

LCD Display Types:

  • Transmissive LCDs: In transmissive construction, all of the light seen by the user comes through the LCD from the backlight. Most LCDs used in portable computers today are transmissive. A transmissive LCD looks good indoors and is typically completely black (unreadable) in direct sunlight. The reason is that sunlight is up to 1,000 times brighter than LCD’s backlight, so the reflection of sunlight from the surface of the LCD overwhelms any light coming through the LCD.

Transmissive

  • Transflective LCDs: Transflective construction starts with a transmissive LCD and adds a partially reflective mirror layer between the LCD and the backlight. Depending on the LCD manufacturer, the mirror layer can be either a half-silvered mirror or a full mirror with tiny holes punched in it. When a transflective LCD is used indoors, it is illuminated by the backlight just like a transmissive LCD, except that the mirror layer blocks some of the light. When a transflective LCD is used outdoors, ambient light reflects off the mirror layer and illuminates the LCD. Note that outdoors, light has to go through the LCD twice, once on the way in and once on the way out. This tends to makes the outdoor performance of a transflective LCD not as good as the indoor performance, where the light only has to go through the LCD once.

Transreflective

A transflective LCD is therefore by definition a compromise. It can never be as bright as a transmissive LCD indoors, and it can never be as bright as a reflective LCD outdoors. It’s particularly poor at the “crossover point”, where there’s enough light outdoors to overpower the backlight, but not enough to fully illuminate the LCD by reflected light. Whether the compromise is acceptable or not depends on how badly the user wants or needs to be able to use the LCD both indoors and outdoors.

  • Reflective LCDs: A reflective LCD always has a fully reflective mirror layer. All light used to view the LCD, whether it’s ambient light or from a frontlight, goes through the LCD, bounces off the mirror layer and goes through the LCD again. (See the sidebar on “Light Guides” for an explanation of how frontlights work.) Since the light still has to go through the LCD (and the frontlight) twice, even though the mirror reflectivity is 100%, the outdoor performance of a reflective TFT with frontlight is generally slightly worse than a transflective TFT (assuming that the same technology is used in both). Indoors, since a frontlight is not as efficient as a backlight, and the light still has to go through the LCD twice, the performance of a reflective TFT with frontlight is again slightly worse than a transflective TFT (once more assuming that the same technology is used in both).

Reflective

The article has been taken from this link, so many thanks to the author. 😉