The standard also defines four levels of quality. Class 1, the highest, allows no defects at all. Class 4, the lowest, allows up to 262! Fortunately nobody refers to it. Apart from some exceptions, all manufacturers refer to Class 2. If they do not specify, the monitor is Class 1 by default and you can have it changed at the smallest pixel defect.
The standard distinguishes four types of defective pixel.
* Type 1: number of always-lit pixels.
* Type 2: number of always-unlit pixels.
* Type 3: other defects, particularly on sub-pixels and the RGB cells making up pixels (lit or unlit). This means red, green and blue pixels lit the whole time. Experience shows that this is undoubtedly the most common defect.
To find the total number of defective pixels allowed, add up the defects of Types 1, 2 and 3.
* Type 4 (Fault Cluster): the number of defective pixels in a square of 5 x 5 pixels on a panel.
Lastly, the standard stipulates the number of errors allowed per million pixels on the panel. More dead pixels are allowed on a 17" screen than on a 15" one.
ISO Standard: The Actual Figures
These are all laid out in a table.