Velleman MONSCA4N - Manual

Information sheet
Velleman ® 1/3 Last update: 25/05/2010
Display Defects
1. Introduction
This information sheet gives more information on how to recognize display defects and determine whether a
display conforms to quality standards.
A TFT LCD monitor consists of multiple layers (see figure below).
1 glass substrates
2 horizontal polarizer
3 vertical polarizer
4 RGB colour mask
5 horizontal control wires
6 vertical control wires
7 polymer layers
8 spacers
9 Thin Film Transistors (TFT)
10 front electrode
11 rear electrode
Display defects can be caused by contamination that entered between layers either during production or
during use, short-circuits between control wires that either keep a pixel or one colour of a pixel dark or
bright, faulty control wires that keep a whole line of pixels turned on or off, scratches on polarizer or glass
substrate caused by mistreatment, dents …
A monitor contains millions of pixels (e.g. MONSCA6: 1280x1040=1,331,200), making it technical nearly
impossible to produce a display without pixel defects. Therefore certain standards were created describing
the number, size, location… of above mentioned defects that are acceptable (allowed) in a TFT LCD display.
For some industries (e.g. aviation) these standards are much more stringent than for others.
2. Definitions
Bright dot defect
Pixels or sub-pixels that appear bright and are visible through a 5% ND (Neutral Density) filter
when a black pattern is displayed. Note that the ND filter must be held parallel to the surface at
a distance of 2.5 to 3 cm.
BM (black matrix) defect
White points on a display that is switched off.
Dark/bright spot
Points on the display that appear dark or bright, usually due to contaminations. These spots do
not change in size or intensity when adjusting the contrast.
Dark/bright lines
Lines on the display that appear dark or bright, usually due to contaminations.
Dark dot defect
Pixels or sub-pixels that appear dark when an RGB coloured pattern is displayed.