Листовка для MicroScreen 15.4" LCD WXGA MSC33025
Модели
MSC33025
LCD Quality Standards
Industry Standards for LCD Screens
The following page sets out laptop screen industry standards with regards to dead pixels and provides
background information regarding LCD screen technology.
Dead Pixels
LCD (liquid crystal display) screens come in various sizes and resolutions. Resolution is defined as the
number of pixels or small dots that make up an LCD screen. The pixel is the smallest unit that makes
up an image. Most screens sold today are TFT active matrix LCD screens. TFT active matrix is a
technology in which each pixel has a transistor attached to it to control the backlight shining through.
Each pixel is made up of 3 sub-pixels (red, green and blue) with each having its own transistor. Each
of these pixels turns on and off and filters light through colored sub-pixels which results in an image.
Occasionally, these individual transistors will short or remain open resulting in a dead pixel. There are
two occurrences which define a dead pixel: a "lit" pixel, which appears as one of several randomly,
placed white, red, blue and/or green pixel elements on a dark background; or a "missing" pixel, which
number of pixels or small dots that make up an LCD screen. The pixel is the smallest unit that makes
up an image. Most screens sold today are TFT active matrix LCD screens. TFT active matrix is a
technology in which each pixel has a transistor attached to it to control the backlight shining through.
Each pixel is made up of 3 sub-pixels (red, green and blue) with each having its own transistor. Each
of these pixels turns on and off and filters light through colored sub-pixels which results in an image.
Occasionally, these individual transistors will short or remain open resulting in a dead pixel. There are
two occurrences which define a dead pixel: a "lit" pixel, which appears as one of several randomly,
placed white, red, blue and/or green pixel elements on a dark background; or a "missing" pixel, which
appears as a black dot on light-colored background.
Considering the number of pixels contained in an LCD panel, the defective rate should dead pixels be
present is usually quite minute. For a typical laptop screen, a 14.1" screen with XGA resolution (1024
x 768 pixels), has a total of 2,359,296 red, green and blue pixels (1024 x 768 x 3). So a screen with 5
present is usually quite minute. For a typical laptop screen, a 14.1" screen with XGA resolution (1024
x 768 pixels), has a total of 2,359,296 red, green and blue pixels (1024 x 768 x 3). So a screen with 5
dead sub-pixels has a defective rate equal to 0.0002%.
Why has the industry established an acceptable level of dead pixels?
To better answer this question, a comparison between a TFT active matrix LCD screen and a CRT
monitor will help illustrate why the market players have established standards for LCD screens.
Pixel defects can be noted in both CRT monitors and LCD screens. During the manufacturing process
for both CRT monitors and LCD screens, pixel outage is difficult to assess. Only upon completed
assembly can an individual display be assessed for dead pixels. The more units classified as defective
in a production line due to pixel malfunction, the lower the overall yield. The lower the overall yield
results in scrapped materials from those defective units and therefore higher production costs. With
higher volume production and lower material costs as well as improved manufacturing methods for
CRT monitors, if there is a decrease in yield it has a minimal effect. However, for LCD screens which
have lower production yields and higher material costs based on current manufacturing methods,
every attempt is made to reduce the number of scrapped displays. The higher production cost of LCD
screens is the main reason this issue is more prominent with LCDs than it has been with CRT
for both CRT monitors and LCD screens, pixel outage is difficult to assess. Only upon completed
assembly can an individual display be assessed for dead pixels. The more units classified as defective
in a production line due to pixel malfunction, the lower the overall yield. The lower the overall yield
results in scrapped materials from those defective units and therefore higher production costs. With
higher volume production and lower material costs as well as improved manufacturing methods for
CRT monitors, if there is a decrease in yield it has a minimal effect. However, for LCD screens which
have lower production yields and higher material costs based on current manufacturing methods,
every attempt is made to reduce the number of scrapped displays. The higher production cost of LCD
screens is the main reason this issue is more prominent with LCDs than it has been with CRT
monitors.
As a result of higher production costs of LCD screens, like their CRT counterparts, LCD manufacturers
and laptop makers have set limits as to how many defective pixels are acceptable for a given LCD
panel, based on user feedback and manufacturing cost data. The goal in setting these limits is to
maintain reasonable product pricing while minimizing distraction from defective pixels for maximum
user comfort. LCD screen manufacturers (i.e. Hitachi, LG. Philips, Samsung and Sharp) and laptop
makers (i.e. Apple, Compaq, Dell, IBM and Sony) have worked together to strike a balance between
functionality of a screen and affordability of a laptop. The very price that a customer has paid for a
laptop computer is directly related to the dead pixel limits set by these industry players. The cost of
accepting only perfect displays could nearly double the price of a portable computer using an LCD
and laptop makers have set limits as to how many defective pixels are acceptable for a given LCD
panel, based on user feedback and manufacturing cost data. The goal in setting these limits is to
maintain reasonable product pricing while minimizing distraction from defective pixels for maximum
user comfort. LCD screen manufacturers (i.e. Hitachi, LG. Philips, Samsung and Sharp) and laptop
makers (i.e. Apple, Compaq, Dell, IBM and Sony) have worked together to strike a balance between
functionality of a screen and affordability of a laptop. The very price that a customer has paid for a
laptop computer is directly related to the dead pixel limits set by these industry players. The cost of
accepting only perfect displays could nearly double the price of a portable computer using an LCD
screen. This is true of all laptop computers using LCD technology.