Twisted nematic or TN LCD panel is a type of thin-film transistor liquid crystal display or TFT-LCD that is commonly used in an array of consumer electronic devices such as digital watches and calculators, as well as computer monitors and mobile phones.
However, further demands for better and wider display applications resulted in the emergence of newer display technologies such as in-plane switching or IPS LCD technology and active-matrix organic light-emitting diode or AMOLED technology.
Nonetheless, it cannot be denied that the introduction of TN technology during the 1970s was a major technological breakthrough because it commercialized the use of LCD and made the use of digital electronic displays in consumer electronic devices affordable and practical.
This article enumerates and discusses the critical advantages and disadvantages of twisted nematic LCD technology.
Explaining TN LCD technology
Central to the technology behind twisted nematic or TN display panel is the use of nematic liquid crystal sandwiched between two plates of glass substrates coated with transparent indium-tin-oxide or ITO. This ITO surface are further coated with alignment layers that both rub in one direction.
The rubbing orients the liquid crystal molecules parallel to the rubbing direction. Because the rubbing directions on the two glass substrates are perpendicular to each other, a 90-degree twist of director from one glass substrate to the other is formed inside the cell.
Manipulation of polarised light is the underlying technological principle behind TN display. When light enters the TN cell, the polarisation state twists with the director of the liquid crystal material.
Advantages of TN LCD panel
The inherent advantages of TN LCD panels made twisted nematic LCD technology a dominant and almost universal display technology used in portable electronics during the 1990s. Take note of the following advantages of TN LCD panels over other display technologies:
1. Inexpensive cost and price: One of the key advantages of TN LCD panels stems from the easy implementation of twisted nematic technology. This translates to cheaper manufacturing requirements and simpler production processes, thus further translating into affordability of TN LCD panels and the corresponding consumer electronics products to end consumers.
Note that the introduction and subsequent popularity of twisted nematic technology quickly pushed out other display technologies such as monolithic LED and CRT for most electronics.
Furthermore, because TN LCD panels are easy and cheap to manufacture, not only did they replace LED and CRT display but they have also continued to remain an affordable alternative to modern display technologies such as IPS and AMOLED.
2. Low power consumption: Twisted nematic technology does not require a current to flow to operate. It also runs under low operating voltages. These advantages collectively correspond to low and efficient power consumption, thus making TN LCD panels suitable for use with batteries and low-powered devices.
The power consumption advantage of TN LCD panels has ushered in the era for low-powered and lightweight LCD, thus paving the way for the invention and production of compact and lighter consumer electronics and non-consumer electronic instruments.
3. Better response time and refresh rate: Pixel response time is the duration it takes a single pixel to transition from one state to another. Measured in milliseconds, the lower the number, the better.
On the other hand, refresh rate is the frequency in which the image in a display is refreshed. Measured in hertz, the higher the number, the better.
High response time and low refresh rates create ghosting effects and motion blurs around an image. This is especially true for fast moving images.
Compared against IPS LCD panels, TN LCD panels have shorter response time and higher refresh rate. Pixels in a typical TN LCD panel change their state as fast as two milliseconds compared against the five milliseconds response time of a typical IPS LCD panel. Furthermore, high-end TN LCD panels even have double the usual refresh rate of 120Hz instead of 60Hz.
The better pixel response time and refresh rate advantages of TN LCD panels can enable them to display twice as much information every second. These make TN LCD panels suitable for use in high-end gaming. In fact, some hardcore gamers prefer a TN computer monitor to a VA or IPS monitor due to its responsiveness and better refresh rate.
Disadvantages of TN LCD panel
The disadvantages of twisted nematic LCD technology have prevented it from catapulting into more modern and wider applications however. Take note of the following limitations and disadvantages of TN LCD panels:
1. Poor viewing angle: A notable disadvantage of TN LCD panels is a narrow viewing angle. A user needs to look at a TN panel from a straight up 90-degree angle to maximize its visual performance.
When viewed from other angles, colors will appear duller and images will appear darker on a TN panel. User familiar with different types of LCD can easily discern if a panel is a TN panel through these color shifts and image distortion.
Nonetheless, the restricted viewing angle compels a user to remain sitting dead straight up in front of a TN LCD panel. Doing so can be problematic in larger TN LCD panels in which changing viewing angle is sometimes unavoidable.
2. Poor color reproduction: Among the different types of LCD to include VA panels and IPS panels, TN panels suffer from poor color reproduction.
Apart from the inherent dull color reproduction in twisted nematic LCD technology, especially when compared against vertical alignment or in-plane switching LCD technologies, the problem with the limited viewing angle also produces poor representation of colors.
Poor color reproduction also means that color inaccuracy is another disadvantage of TN panels. This is the reason why TN panels are not suitable for use in color critical tasks such as graphic design, photo manipulation, and video editing, among others.
3. Quality variability: Note that the quality of TN LCD panels depends on manufacturers. Low-end TN LCD panels have the tendency to exhibit extreme instances of other disadvantages such as poor viewing angle and poor color reproduction.
Take note of cheap feature mobile phones as an example. The TN LCD panels used in these products can exhibit extreme color shifts even at slight change in viewing angle.
Images in low-end TN LCD panels can also be indiscernible when viewed under direct sunlight. Note than another disadvantage of TN LCD panels is susceptibility to dead pixels. This becomes more pronounced in cheaper and low-end panels.
Conclusion: Advantages and disadvantages of TN LCD panel
Twisted nematic LCD technology was a breakthrough innovation that paved the way for an array of relatively inexpensive electronic devices that use digital electronic display. TN panels remain a very popular LCD option because of their advantages that revolve around inexpensive manufacturing and simpler production that translate further to cheaper price points for end consumers.
However, TN panels are becoming noticeable archaic due to the popularity of other display technologies such as in-plane switching or IPS LCD technology and active-matrix organic light-emitting diode or AMOLED technology. Both technologies are becoming more prominent in modern consumer electronics such as smartphones and tablet computers.
Of course, the associated cost efficiency of producing and using TN panels, in addition to other advantages such as low power consumption and better response time and refresh rates, still make them an ideal display option for use in inexpensive computer monitors, as well as for other portable electronics such as digital watches and calculators.
Further readings: Several information from the article are culled from the following scholarly articles: (1) Kim, K. H. & Song, K. J. (2009). “Technical evolution of liquid crystal displays.” NPG Asia Materials. 1(1). DOI: 10.1038/asiamat.2009.3