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Pixel Defects on TFTs (LCD-Displays)
Active matrix TFTs (LCD) with a resolution of
1440 x 900 pixel (WSXGA)
, which are in turn composed of three
sub-pixels each (red, green, blue), contain
about 3.9 million
addressable transistors. Because of this very high
number of transistors and their extremely complex production process occasionally defective or incorrectly ad-
dressed pixels or sub-pixels may occur.
There have been several attempts in the past to define the acceptable number of defective pixels. But this can be
difficult and varies widely between different manufacturers.
MEDION, therefore, adheres to the clear and strict requirements of
ISO 13406-
2, class II
, for the warranty handling of all TFT display products. These re-
quirements are summarized below.
Within ISO-standard 13406-2 the general requirements regarding pixel defects
are defined. Pixel defects are classified into three failure types and four failure
classes. Each individual pixel is made up of three sub-pixels in the primary
colors (red, green, blue).
Types of Pixel Failures:
•
Type 1:
A constantly lit pixel (a bright, white spot), even though it is
not
addressed
A white pixel is caused when all three sub-pixel are lit.
•
Type 2:
A pixel that does not light up (dark, black spot), although it is addressed
•
Type 3:
Abnormal or defective red, green or blue sub-pixels.
(E.g. constantly lit with half the brightness, one color is not shining, blinking or flickering, but not belonging to
Type 1 or 2 Pixel Failures)
In addition:
A cluster of type 3 (= 2 or more defective sub-pixels in an array of 5 x 5 pixel). A cluster is an array
of 5 x 5 pixel (15 x 5 sub-pixel).
Classes of Pixel Failures:
Failure class
Type 1 Type 2 Type 3 Cluster v. Type 3
I
0
0
0
-
0
II
2 2 5 - 2
III
5
15
50
5
IV
50
150
500
50
The acceptable number of defects of the above mentioned types in each failure class refers to one million pixels
and has to be calculated according the physical resolution of the display.
This leads to a maximum
allowed
number in
class II type failure:
Resolution
Mn Pixel
Sub-Pixel
(Type s. above)
1024 x 768 (15")
0.786432
2.359296
2 2 4 - 2
1280 x 1024 (17,18, 19")
1.310720
3.932160
3 3 7 - 3
1600 x 1200 (19“)
1.920000
5.760000
4 4 10 - 4
1440 x 900 (19“ wide)
1.296000
3.888000
3 3 7 - 3
1680 x 1050 (20“ wide, 22“ wide)
1.764000
5.292000
4 4 10 - 4
Class I type failure only applies to special applications, e.g. medical applications, and results in corresponding price
increases. Class II type failure is the established standard for quality conscious manufacturers with high quality
displays.
Rows
Blue
Green
Red
