Liquid crystal display has become increasingly popular in the creation of television and computer screens and is also in telephones and watches. This technology offers a thinner and lighter weight alternative to the traditional CRT displays. However, LCD electronics do have some common faults that consumers should take into consideration when purchasing an LCD device.
LCD displays consist of thousands of dots known as pixels and inside each pixel are three coloured (red, green and blue) sub-pixels. Pixels work in combination to present the overall image on the screen. A dead or defective pixel occurs when a pixel remains black, white or coloured, regardless of the image on the screen. Dead pixels are more difficult for the user to see on larger screens and when the display is further away from the user. However, users can more readily detect dead pixels on smaller screens, such as a computer monitor. Manufacturers classify displays by the number of dead pixels per million pixels. For example, a Class II LCD screen may have between one and five dead pixels per million pixels. These defective pixels may occur at production or may develop over time.
LCD television and monitor owners will notice that the contrast and colours on their LCD devices vary depending on the angle at which the user is viewing the screen. Other types of displays, including CRT televisions, do not experience this effect. The user will experience the best picture when viewing the LCD screen from the manufacturer-recommend vertical angle. If the viewer's line of sight is above or below this angle, the image contrast decreases. The reduction of contrast that occurs when the user is not at the optimum viewing angle can make it difficult to read text on the screen or differentiate between items on the screen.
LCD screens may not display a true black image. In comparison to Plasma televisions or LCD and LED combination screens, the black levels that LCD screens display may really be a dark grey. This characteristics of LCD devices occurs because the light source in an LCD display is always on. CNET editors explain that their LCD monitor testing includes a screen that examines the device's ability to display true white and true black levels. This is because "These outermost edges are the most difficult part of the scale for LCDs to produce."
LCD televisions and monitors require a compound known as nitrogen trifluoride (NF3) during the etching stage of production. NF3 is a greenhouse gas that could potential contribute to global warming and the decrease of the ozone layer. While the cleaning processes destroy the majority of this compound, atmospheric scientist Michael Prather cautions that experts should be monitoring and measuring the atmospheric levels of NF3 to determine the effect of the increasing use of this agent and its long half-life are contributing factors of global warming.