Most monitors sold today use a Twisted Nematic (TN) LCD panel. The advantage of this LCD technology is that it is cheap to produce and that TN panels can change state quickly, giving them the best response time of all available LCD technologies. This makes the panels more appropriate for games that render fast image transitions. Thanks to the combination of low cost and rapid response time, TN displays are by far the most popular today.
How Does a TN LCD Work?
The discovery of the TN effect was a revolution in flat screen technology and for all intents and purposes is it what brought LCD technology into the mainstream. The effect means that the liquid crystals are controlled and restructured into different molecular configurations under the influence of an electrical field. It requires that the liquid crystals can be turned between “on” and “off” states. This is achieved by letting the current pass through layers of film (hence the name Thin Film Transistor, or TFT). Twisting it 90 degrees lets no light through, whereas another state lets though the specific sub-pixel colors red, green or blue (RGB). If the red, green and blue sub-pixels are all fully lit, the pixel turns white.
The virtues of the Twisted Nematic technology include the lowest response times among modern flat screen displays, as well as a low production cost. The downsides–at least in early generations–are poor color rendition and narrow viewing angles.
The different layers of an LCD monitor can be seen on the right: The first is a vertical film that polarizes the incoming light, the second layer is a substrate with electrodes, the shapes of which will determine what shapes that appear on the screen. Layer number three is the one that is made up of Twisted Nematic crystals that control the flow of molecules. The fourth is another glass substrate; unlike the first, which is the vertical polarizing filter, this layer acts as the horizontal filter. The final layer is the surface that absorbs and retransmits the light source, whether it comes from more modern and power-efficient LEDs or compact fluorescents (image credit: Wikimedia Commons).
TN Panel Pros and Cons
As previously mentioned, viewing angles and color reproduction are not areas where TN panels excel compared to other, more expensive displays. Seen from a steep angle, the image discolors quickly; viewed from below the picture can be very dark and looking at it too far from the top, the contrast can reverse itself, allowing light to dark shades and vice versa.
Although TN panels and monitors with this technology has great strides in recent years, the color accuracy is not on par with monitors using In Plane Switching (IPS) and Patterned Vertical Alignment (PVA) panels. On the other hand there are some significant drawbacks with these panels too.
First of all, they are more expensive than TN, and IPS, PVA and other high-end alternatives are less suitable for gamers, as they tend to have higher (=worse) response times. However, for color critical applications such as photography, video editing or web design, monitors with IPS and PVA are still the best choice.
Other weaknesses of TN is the moderate levels of contrast and the ability to produce blacks and whites accurately. However, today’s monitors are considerably better in this respect than they were just a few years ago.