Defective pixels are pixels on a liquid crystal display (LCD) that are not performing as expected, failing to reproduce light levels correctly. The ISO standard ISO 13406-2 distinguishes between three different types of defective pixels, while hardware companies tend to have further distinguishing types.
Variations
Dark dot defects
A dark dot defect is usually caused by a transistor in the transparent electrode layer that is stuck "on" for TN panels or "off" for MVA/PVA and IPS panels. In that state, the transistor places the liquid crystal material in such a way that no light ever passes through to the RGB layer of the display.
Bright dot defects
A bright dot defect is a group of three sub-pixels (one pixel) all of whose transistors are "off" for TN panels or stuck "on" for MVA/PVA panels. This allows all light to pass through to the RGB layer, creating a bright white pixel that is always on. This is commonly known as a "hot pixel".
Partial sub-pixel defects
A partial sub-pixel defect is a manufacturing defect in which the RGB film layer was not cut properly.
Stuck sub-pixels
A stuck sub-pixel is a pixel that is always "on". This is usually caused by a transistor that is not getting any power, and is therefore continuously allowing light at that point to pass through to the RGB layer. This means that any given pixel will stay red, blue, or green, and will not change when attempting to display an image. These pixels may only show up using certain applications, or they may be on all of the time.
Stuck versus dead pixels
Stuck pixels are often incorrectly referred to as "dead pixels", which have a similar appearance. In a dead pixel, all three sub-pixels are permanently off, producing a pixel which is permanently black. Dead pixels can result from similar manufacturing anomalies as stuck pixels, but may also occur from a non-functioning transistor resulting in complete lack of power to the pixel. Dead pixels are much less likely to correct themselves over time or be repaired through any of several popular methods.
Stuck pixels, unlike dead pixels, have been reported by LCD screen owners to disappear, and there are several popular methods purported to fix them, such as gently rubbing the screen (in an attempt to reset the pixel), cycling the color value of the stuck pixel rapidly (in other words, flashing bright colors on the screen), or simply tolerating the stuck pixel until it disappears (which can take anywhere from a day to years). While these methods can work on some stuck pixels others cannot be fixed by the above methods. Also, some stuck pixels will reappear after being fixed if the screen is left off for several hours.
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