S
S
P
PE
EC
CIIFFIIC
CA
AT
TIIO
ON
NS
S
17
P
IXEL
D
EFECTS ON
LCD
S
(TFT-D
ISPLAYS
)
Active matrix LCDs (TFT) with a resolution of 1024 x 768 pixel (XGA), which are in turn composed of three sub-pixels
each (red, green, blue), contain about 2.4 million addressable transistors. Because of this very high number of tran-
sistors and their extremely complex production process occasionally defective or incorrectly addressed 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 require-
ments 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 belong-
ing 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 Mill.
Pixel SubPixel 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
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 dis-
plays.
Example 1:
A 15” - XGA-display consists of 1024 horizontal and 768 vertical picture dots (pixel), which amounts to a total of
786,432 pixel. Related to one million pixels this translates into a factor of about 0.8.
Class II type failure consequently allows for two defects each of type 1 and type 2 and 4 defects of type 3 and 2
clusters of type 3.
Example 2:
A 17” - SXGA-display consists of 1280 horizontal and 1024 vertical picture dots (pixel), which amounts to a total of
1,31 million pixels. Based on one million pixels this translates into a factor of about 1.31.
Class II type failure consequently allows for three defects each of type 1 and type 2 and 7 defects of type 3 and 3
cluster of type 3.
These cases are normally not covered by warranty.
If the number of failures exceeds the figures of any category mentioned above then this may be covered by the
warranty.
Rows
Blue
Green
Red
