LCD Displays with Dead Pixels
A defective pixel, or dead pixel, on an LCD display is a pixel that is not functioning correctly. The ISO standard ISO 13406-2 distinguishes between different types of defective pixels. One common type is the dark dot defect, which usually occurs when a transistor in the transparent electrode layer is stuck on for TN panels or off for MVA, PVA, and IPS panels. In this state, the liquid crystal material does not rotate, preventing the backlight from passing through the RGB layer and resulting in a dark dot on the screen.
Another type is the bright dot defect, also known as a hot pixel, where all three sub-pixels of a pixel are stuck on for MVA and PVA panels or off for TN panels, allowing all light to pass through and creating a constantly bright pixel. Impurities in the liquid crystal can also cause bright spots by affecting the alignment of liquid crystal molecules and reflecting light.
Manufacturers have different policies regarding defective pixels. Some have a zero-tolerance policy and reject any display with even a single defective pixel, while others tolerate a certain number of faulty pixels depending on the class of the display. In some cases, manufacturers may send all screens to market and replace them if the customer reports a problem and the defective pixels meet the minimum return requirements.
Dead pixels can be a nuisance, especially for users who require a high-quality display. However, it is important to note that a small number of defective pixels may not significantly affect the overall usability of the display, depending on their location and the specific application.
