LCD Panel Types Explored

Author: Adam Simmons
Last updated: November 19th 2016

 

Like our articles? Please help support the website by purchasing your monitor or other computer peripherals and components using the ‘Buy from’ links found in select posts, reviews and the recommendations section.


Introduction

Most people are familiar with the fact that monitors come in various resolutions and screen sizes, can have a matte or glossy screen surface and can offer specific features such as 120Hz refresh rates and 3D capabilities. The range of displays and variation in specification can be rather daunting and what’s more; you can’t necessarily trust the ‘on paper’ figures in the first place. One fundamentally important aspect of an LCD monitor which will dictate how it performs and what kind of tasks it would be best at performing is the panel type. Although there are various sub-divisions all modern screens will generally fall into one of three categories with distinct performance characteristics.

TN (Twisted Nematic) panels

For several years now the TN panel monitor has been the most ubiquitous on the market. Manufacturers will often be keen to point out in their specifications whether an ‘alternative’ kind of panel is used; if in doubt assume its TN. General attributes include a relatively low manufacturing cost and a relatively high level of responsiveness; the pixels change their state quickly which helps make moving images appear smoother. Some Twisted Nematic displays have double the usual refresh rate (120Hz instead of 60Hz) allowing them to take advantage of ‘active 3D shutter’ technologies and allowing them to display twice as much information every second for a smoother gaming experience. This has gone a stage further more recently with some models promoting a 144Hz refresh rate and aiming this purely at a fluid 2D rather than 3D experience.

The BenQ XL2420Z – a 144Hz TN panel monitor

The BenQ XL2420Z – a 144Hz TN panel monitor

Although it has improved leaps and bounds in this department over the years the image performance is often considered a relative weakness of TN technology. A good TN monitor can provide a crisp and vibrant image with respectable contrast – typically 1000:1 with any ‘dynamic contrast’ mode disabled. The main drawback comes with relatively restricted viewing angles. These are often quoted as 170 degrees horizontal and 160 degrees vertical which is only marginally lower than that quoted for other panel technologies. In actuality you will see a marked change in colour and even ‘inversion’ if you view the screen from the side but also from above or below, in particular. You can see this shift demonstrated in the video below on what is regarded as quite a capable 27″ TN monitor (the PG278Q ROG SWIFT in this case).


Since these screens are typically relatively large these days (generally up to 28”) the relatively restricted viewing angles actually affect the performance if you are sitting dead in front, too. Your eyes subtend different viewing angles if you observe the centre of the screen vs. one of the peripheral regions. You will see a given colour shade represented slightly differently depending on its position on the screen – most notably being darker towards the top of the screen and lighter towards the bottom. Because of this the colour accuracy and consistency suffers making them a poor choice for ‘colour critical work’ such as design and photography. You can see this in the image below, captured on the ASUS PG278Q in a way that is fairly representative of what you would see when observing the monitor from a normal viewing position at a desk.

Colour shift from a normal viewing position

VA (Vertical Alignment) panels

If an LCD monitor is trying to display black then the colour filter will be positioned such that as little light as possible (of any colour) from the backlight will get through. Most LCD monitors will do a reasonable job at this but the filter isn’t perfect and so the blacks may not appear as deep as they should. A definite strength of the VA panel is its efficiency at blocking light from the backlight when it’s not wanted. This gives deeper blacks and higher contrast ratios of around 2000:1 – 5000:1 with ‘dynamic contrast’ modes disabled – several times higher than that of the other LCD technologies. They are also less susceptible to ‘bleed’ or ‘clouding’ towards the edges of the screen which can make such screens good candidates for movie lovers and nice to use for general purpose work.

The BenQ GW series – modern VA panel monitors

The BenQ GW series – modern VA panel monitors

Another key advantage of VA is the improved viewing angles and colour reproduction compared to TN. The shift in colour across the screen and ‘off angle’ is less pronounced whilst shades can be produced with greater precision. In this respect they are better candidates for ‘colour critical work’ but they are not as strong in this area as the IPS or PLS technologies explored subsequently. There is generally a weakening of saturation when comparing a shade in the centre of the screen vs. that same shade towards the edges or bottom of the screen, from a normal viewing angle. There is also a shift in gamma that is most noticeable on greys but can also be observed on other shades, with said shade appearing to lighten or darken quite readily with even slight head movement.

It isn’t cost that has traditionally been the main weakness of the VA panel as they are typically fairly affordable with a good modern range available from companies such as Philips, Iiyama, BenQ and Samsung. The real weakness comes in their relatively low level of responsiveness with pixels transitioning from one state to another relatively slowly – leading to more pronounced blurring during fast motion. In some severe cases things can appear to ‘smear’ into a smoke-like trail as demonstrated in the video below, taken on a BenQ EW2430.


Some of the modern VA panel types used on PC monitors include MVA (Multi-domain Vertical Alignment), AMVA (Advanced MVA) or AMVA+ (AMVA with slightly enhanced viewing angles). Recent AMVA(+) models generally use effective pixel overdrive and don’t suffer from these extensive ‘smoke-like’ trails. They are actually on par with modern IPS models during some pixel transitions. Other pixel transitions, typically between light colours and dark bold colours, are still relatively slow – but not to the extent demonstrated in the video above. We were also rather impressed by the performance of the Samsung S34E790C, which generally performed better than one of its IPS counterparts (the Dell U3415W) when it came to responsiveness.

Panel manufacturer AU Optronics (AUO) have created a 35″ ‘UltraWide’ VA panel with 144Hz refresh rate, something used in the likes of the BenQ XR3501 and Acer Z35. Despite the high refresh rate, some pixel transitions were again notably sluggish. Both AUO and Samsung are producing various other 100Hz+ VA panels as well. Sharp have some specialist MVA panels used on a few models including the FG2421 that natively support 120Hz. Doubling the refresh rate alone is only so good if the pixels can’t really keep up, though. To help overcome these limitations monitors using the Sharp panel employ a strobe backlight combined with frame rate doubling (something called ‘Turbo240’) to essentially hide a lot of the pixel transition behaviour and reduce eye-tracking motion blur. These concepts are discussed in detail in our dedicated responsiveness article.

IPS (In-Plane Switching), PLS (Plane to Line Switching) and AHVA (Advanced Hyper-Viewing Angle) panels

When it comes to the end result these three technologies are essentially very similar; the key differences being that IPS technology is developed chiefly by LG Display, PLS technology by Samsung and AHVA by AUO. These are sometimes simply referred to collectively as ‘IPS-type’ panels. The real selling point of these is their superior colour accuracy, consistency and viewing angles when compared to the other LCD technologies. Each colour shade remains distinct with its own ‘identity’ regardless of its position on the screen. Some of the higher-end IPS and PLS models take things even further by offering support for extended colour gamuts (increasing potential shade range) and higher colour depths (increasing potential accuracy). This makes IPS and PLS panels good candidates for ‘colour critical’ work in particular. It is also common for larger IPS monitors to feature higher resolutions than most of their TN and VA counterparts; although a good range of resolutions for all panel types is now available. The choice of resolutions, ever-decreasing price and colour performance really broadens their appeal beyond just ‘colour critical’ work and makes them attractive candidates for other uses including gaming and general desktop work.

The AOC i2369Vm - IPS doesn't have to be expensive

The AOC i2369Vm - IPS doesn't have to be expensive



There is actually a very good range of affordable IPS monitors available from manufactures such as Dell, LG, AOC and ASUS. This means that photographers or designers or just regular users on a lower budget can take advantage of the technology too. Many modern IPS and PLS monitors are also far more responsive than their VA counterparts and will even rival some TN monitors. This was traditionally an area of significant weakness for IPS panels. Due to these dramatic improvements some modern models have found favour amongst gamers who take advantage of the colour performance in their favourite titles without lots of unsightly trailing. The pixel responsiveness has actually now reached a level on some modern IPS or IPS-type models where the level of motion blur as as low as you’ll see on any 60Hz LCD monitor, as we explore in this article. Responsiveness is not quite up to the task of optimal performance at 120Hz+ refresh rates, although being able to make a decent go of a refresh rate and performing optimally are two seperate things. Indeed, sufficient improvements have been made in those areas that the AUO and LG are releasing IPS-type panels with 144Hz+ refresh rates. Another area of traditional weakness was contrast. They have certainly improved in this area and are typically similar to their TN counterparts in that department now (around 1000:1 contrast ratio without dynamic contrast). One troublesome issue that some people have noticed is a sheen or ‘glow’ when viewing dark content that is caused by the behaviour of light in these panels. This is typically most obvious when viewing ‘off angle’ as shown on the Samsung S27A850D in the video below. You will generally be able to observe this on the corners of 21.5″+ models whilst viewing from directly in front, unless you are sitting quite far back from the screen. The majority of time you will be looking at brighter and more colourful shades where these displays excel but it is always worth looking beyond figures on paper.


Conclusion

There are three main categories of panel used on modern LCD monitors; TN, VA and IPS-type. TN is currently the most prevalent, offering decent image performance and high responsiveness at a decent price. VA sacrifices responsiveness, generally being the slowest current panel type but offer excellent contrast and improvements in colour performance over TN technologies. IPS, PLS and AHVA are the kings of colour offering the most consistent and accurate performance in this area whilst sporting excellent viewing angles, respectable responsiveness and reasonable contrast. Really it is up to the individual user to weigh up the advantages and disadvantages of the monitors they are comparing; understanding the general performance characteristics of different panels is a great starting point.

Further reading

  • This post explores some of the key points of comparison between IPS and VA panels. Further discussion is included later on in that thread. The video below, taken from this thread, offers a good summary of these key differences.



  • The video below offers a visual comparison between an IPS-type panel and a TN panel. First perceived contrast differences are discussed and demonstrated, then colour performance is analysed in a similar way.