Manufacturers of LCDs came to the conclusion a few years back that, if they lowered their quality standards and accepted having a few bad pixels in an LCD monitor, they could divert numerous LCD monitors from the scrap bin and average down the production cost.
While making some sense, this does mean that it is possible to buy a brand new LCD monitor that has pixels in its array that are either not working, or are stuck on. The acceptable number of misbehaving pixels is up to the manufacturer. Each has what is known as a "pixel policy".
Here is the pixel policy of Viewsonic (as of March 12, 2003), along with an explanation of the technology.
Viewsonic LCD Pixel Criteria...
ViewSonic is committed to customer satisfaction by providing the highest quality products in the industry. The result is that our LCD displays generally have very few non-performing pixels. For example, an 18" SXGA (1280 x 1024) display has nearly 4 million sub-pixels. A product exhibiting 7 non-performing pixels would equate to an extremely small 0.00018 percent of the total sub-pixels.
(1280 Horizontal Pixels) * (1024 Vertical Pixels) * (3 sub-pixels per pixel) = 3,932,160 sub-pixels
[(7 non-performing pixels) / (3,932,160 sub-pixels)] * 100% = 0.00018%
To ensure the highest performing displays, ViewSonic sets limits as to the allowable number of pixel anomalies. ViewSonic has adopted the following pixel criteria to supplement our existing three-year limited warranty. This policy applies to all ViewSonic LCD display during the warranty period.
ViewSonic sets limits on 14" - 15" LCD's at 4 bright sub-pixels, 4 dark sub-pixels, or a combination of 4. ViewSonic sets limits on 17" - 19" LCD's at 7 bright sub-pixels, 7 dark sub-pixels, or a combination of 7.
ViewSonic sets limits on 20" & greater LCD's at 10 bright sub-pixels, 10 dark sub-pixels, or a combination of 10.
It is possible that any replacement display may also have some non-performing sub-pixels. This should be considered when requesting a warranty exchange.
A pixel or picture element, is composed of three sub-pixels in the primary colors of red, green, and blue. At each pixel position in an AMLCD (active matrix liquid crystal display) flat screen monitor, three cells of liquid crystal material form the red, green and blue sub-pixels that together allow the full range of colors to be displayed. Individual transistors are arranged in an array on the rear glass to control each sub-pixel. An anomaly on any one of these individual transistors will cause a bright or dark pixel to appear. These anomalies generally occur only during manufacturing, and additional bright or dark pixels should not appear over time.
The allowable number of non-performing pixels has a direct impact on the yield of the process. If the industry attempted to set a zero standard, the current manufacturing yield would be so low that the cost of an LCD display would be many times higher than it is today. Luckily, most customers and applications are tolerant of a low level of non-performing pixels and prefer the lower cost that the existing standards allow.
So, be careful which LCD monitor brand you buy, and, if possible, have the product first opened and tested.
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