Introduction
No product is completely free of defects, but LCD monitors have brought the definition of defects to the public light. Imagine how frustrating it can be to bring home a new monitor, turn it on and see a black or white dot in the middle of this new display. Worse yet, there could be three of four of these dots scattered around the display.
As a consumer looking to purchase an LCD monitor for a computer or even to be used as a TV, it is very important to understand your rights with regards to the quality of the item you are purchasing. This article looks to help inform consumers what a pixel defect is, why they are allowed and how to look at warranties.
LCD Basics
To understand how pixel problems develop in an LCD monitor, it is important to have a basic understanding of the underlying technology of the LCD monitor. Unlike CRTs that are actively generating the light through phosphors, an LCD actually takes white light and filters it to get the desired colors. To do this for each given pixel, three sub pixels are defined for red, green and blue light. When the sub-pixel is off, the filter will block the specified color of light. When the sub-pixel is on, it will open the filter to let a desired amount of light through.
Dead and Stuck Pixels
Pixel defects for an LCD monitor are defined as one of two types: dead or stuck. Technically, both types of pixel defects are stuck pixels but it really deals with the electrical currents and the state of each pixel or sub-pixel.
A dead pixel is defined as a pixel or set of sub-pixels that has failed and is permanently in the off position. This condition means that the pixel will not let any light through. This can be observed as a dark or black spot on a brightly colored or white background.
A stuck pixel is defined as a pixel or sub-pixel that has failed and is permanently in the on position. This can be either with a single or multiple sub-pixels for a given pixel and is best observed on a dark or black background. A white pixel means all three sub-pixels have failed while a green, red or blue pixel means one of the sub-pixels has failed.
Why Are Defects Allowed?
LCD panels are very complicated devices to put together. Each pixel in an LCD monitor is controlled by a number of transistors embedded into sheets of material. For example, a 15" LCD with a resolution of 1024x768 has 786,432 pixels comprised of 2,359296 sub-pixels. Monitors with higher resolutions will have an even greater number of pixels. Even a small impurity in the layers that make up these pixels can result in a pixel defect.
If the manufacturers were to throw out every panel that even had a single defect, the cost to produce LCD monitors would be so high that no consumers would be willing to purchase them. To help them financially produce the panels, the manufacturers have defined a certain percentage of pixels that can be defective but still allow them to sell the panel. This percentage is extremely small, equating to under 1/100th of a percent of the total number of pixels. With improved technologies and techniques, the number of panels being produced with defects is dropping.
Warranties
It is important to find out what the replacement policy is on any LCD monitor prior to purchase. In general, the manufacturer will have a policy with regards to the number of stuck or dead pixels allowed before it can be returned. To make things even more confusing, the location of the pixels can also play an important role in whether the manufacturer will accept it as defective. The number of defective pixels that define a panel as meeting the replacement criteria will also vary with the size and even model of the monitor.
In addition to the manufacturer warranty, look at the replacement policy of the retailer that you are purchasing the monitor from. It is very likely that the policy of the retailer may be better than that of the manufacturer allowing another avenue if the newly purchased monitor has a number of defective pixels.
Conclusions
It is very important to be a well informed consumer when purchasing an LCD monitor. Research the warranty and replacement policies from the manufacturer and retailer before making a purchase. Be sure to understand what the terms of the different types and locations of pixel defects mean. All of this can help alleviate frustration if the monitor that you purchase does not meet your standards of quality.
