A display technology that uses rod-shaped molecules (liquid crystals) which flow like liquid and bend light. Unenergized, the crystals direct light through two polarizing filters, allowing a natural background color to show. When energized, they redirect the light to be absorbed in one of the polarizers, causing the dark appearance of crossed polarizers to show. The more the molecules are twisted, the better the contrast and viewing angle. There are three types of LSDs:
1. 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.
Portable computer manufacturers such as Amrel, Intermec, Itronix, Microslate, Panasonic, Xplore and others all claim to have "daylight-readable transmissive LCDs" in their laptop or tablet products. Given the above, how do they do it? One of two basic ways: (a) increase the brightness of the backlight, or (b) modify the LCD to reduce the amount of ambient light that's reflected. See the sidebar on "Making Transmissive TFTs Work Outdoors" for more details.
2. 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.
The balance between outdoor and indoor performance can be adjusted during manufacture of the LCD by varying the reflectivity of the mirror layer. For example, the mirror layer might be set to reflect 60% and transmit 40% of the light.
This means that if the normal indoor brightness of the LCD is 130 nits, only 52 nits (40% of 130) is transmitted from the backlight through the mirror layer and the LCD. Outdoors, 60% of the light hitting the mirror layer is reflected, but since the light has to go through the LCD twice, the user actually sees less. 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.
3. 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). -
Based in Silicon Valley, Geoff Walker is a consultant with Walker Mobile. Geoff has worked on the engineering and marketing of pen computers since 1990 at GRiD Systems, Fujitsu Personal Systems (now Fujitsu PC) and Handspring.
1. 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.
Portable computer manufacturers such as Amrel, Intermec, Itronix, Microslate, Panasonic, Xplore and others all claim to have "daylight-readable transmissive LCDs" in their laptop or tablet products. Given the above, how do they do it? One of two basic ways: (a) increase the brightness of the backlight, or (b) modify the LCD to reduce the amount of ambient light that's reflected. See the sidebar on "Making Transmissive TFTs Work Outdoors" for more details.
2. 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.
The balance between outdoor and indoor performance can be adjusted during manufacture of the LCD by varying the reflectivity of the mirror layer. For example, the mirror layer might be set to reflect 60% and transmit 40% of the light.
This means that if the normal indoor brightness of the LCD is 130 nits, only 52 nits (40% of 130) is transmitted from the backlight through the mirror layer and the LCD. Outdoors, 60% of the light hitting the mirror layer is reflected, but since the light has to go through the LCD twice, the user actually sees less. 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.
3. 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). -
Based in Silicon Valley, Geoff Walker is a consultant with Walker Mobile. Geoff has worked on the engineering and marketing of pen computers since 1990 at GRiD Systems, Fujitsu Personal Systems (now Fujitsu PC) and Handspring.
1 comment:
Wow didnt know there was so much put into building an LCD Screen.
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