The monitor and display market is always evolving, not always as fast as some people would perhaps like, but nevertheless always changing. In recent times you may have started to hear about various new technologies, features and specs and wondered what they are all about. We thought it might be useful to start a short series of guides which take you through some of the buzz-words in the market right now and explain them in a bit more detail.
In this article you can read all about:
- LG.Display’s latest generation of IPS panel technology – Nano IPS
- Quantum Dot which is used for improving a screen’s colour space
- Full Array Local Dimming (FALD) backlights used for HDR displays
In Plane Switching (IPS) panel technology has been around for many years, and has long been the preferred panel technology in LCD monitors for professional displays and for colour critical work. In more recent years IPS has come to be the preferred choice for many consumers who are looking for a screen with strong all-round performance characteristics. IPS has always been characterized by its stable image quality and wide viewing angles. Improvements in response times and refresh rate have also made it a very viable alternative to the more common TN Film technology typically used in gaming displays. LG.Display were the original manufacturer of IPS technology in the early days, but other manufacturers are now also producing their own IPS-type equivalents with very similar characteristics. AU Optronics with their AHVA, and Samsung with their PLS for instance are alternatives to LG.Display’s IPS options.
Over the years IPS has gone through various generations as different aspects are improved, including response times, brightness, viewing angles etc. In 2018 LG.Display, who are still one of the main producers of IPS-type panels, introduced their latest generation of IPS, dubbed “Nano IPS”. The most significant change with this latest Nano IPS generation is the colour space that can be produced by the display.
Traditional IPS panels are usually paired with a W-LED (White LED) backlight unit which allows the screen to produce the colours represented by the common sRGB reference space. This is the typical colour space used by most content and users. There are occasions where people may wish to work with content that is designed with a wider colour space in mind, particularly for professional photography, print etc. In those situations an IPS panel could be paired with a more expensive type of LED backlight (e.g. an RGB LED or GB-r LED unit) which produced a wider colour space, commonly covering the Adobe RGB reference. Those backlights are more expensive, bulky and power hungry though so are reserved for higher end, professional grade displays normally. This is a similar pattern with other panel technologies like VA for instance, where the backlight typically dictated the colour space being offered but also the cost and other factors.
HDR (High Dynamic Range) is a relatively new area to the desktop monitor market, but one important aspect of such content is the need for a colour space beyond the normal sRGB gamut. The colour space now talked about for HDR content is DCI-P3, with a display needing to ideally produce at least 90% of this colour space to properly handle HDR colours. This corresponds to a coverage of around 125 – 135% sRGB and so with the increased interest in HDR, manufacturers needed a more affordable way to offer wider colour spaces from their displays. This has led to the production of a couple of alternate options, one of which is Nano IPS from LG.Display.
In the production of Nano IPS, a layer of nanoparticles (hence the name) is applied to the standard W-LED backlight of the screen. These absorb certain wavelengths of light, for instance absorbing unnecessary yellow and orange which in particular leads to more accurate red shades. From a technical/chemical point of view it is a KSF phosphor layer that is added (K2SiF6 doped with Mn4) and gives rise to the name “KSF LED” to describe the backlight unit. This KSF layer allows Nano IPS panels to offer a wider than normal colour space equating to 98% of the DCI-P3 reference, which is about 135% of the sRGB space. This allows support for HDR content and produces more vivid, bright and saturated colours.
For reference, an alternative method you might hear talked about is “Quantum Dot” (more info below) which is something Samsung are investing in for instance. With Quantum Dot the nanoparticles are applied between the backlight and panel via a special film layer, and not directly to the backlight like with Nano IPS. According to LG.Display this results in a slightly lower DCI-P3 coverage from Quantum Dot displays, although in practice that doesn’t appear to be completely accurate. Our measurements so far of Nano IPS vs Quantum Dot colour spaces has been very similar in the desktop monitor market at least. There are also currently limitations in offering borderless panel designs with Quantum Dot it is stated.
Other than this wider colour space there are no specific changes or improvements over older generation IPS panels being targeted. There are generational improvements in things like response times and refresh rate, but those are not specific characteristics of the Nano IPS technology.
Quantum Dot is an alternative technology for helping to boost the colour gamut of a display, without the need for expensive wide gamut backlights. The most common application in the display market currently is where a very thin film or coating (a “Quantum Dot Enhancement Film” or “QDEF”) is applied between the backlight and panel to help filter the light coming from the backlight and provide more vivid and saturated colours. Rather than use traditional W-LED backlights, a Blue LED backlight is actually used typically.
The Quantum Dots themselves are incredibly small sized particles which range in sizes between 2 and 10 nanometers (nm). The size of the particles varies as that is what dictates the colour produced. The bigger QDs are red and are usually as big as 7nm (150 atoms) in diameter, while green particles are about 3nm (30 atoms) in diameter. Blue QDs are the smallest—their core size is about 2nm (15 atoms) in diameter. Because of their tiny size, blue particles are very vulnerable and challenging to work with. For this reason, red and green QDs are most frequently used in panel technologies.
Quantum Dot coatings can help facilitate higher peak brightness for HDR capable displays while also allowing the support for wider colour spaces.
Samsung have an interesting article about Quantum Dots if you want to read more. Click here
We have already seen a fair number of displays released, including models like the Asus ROG Swift PG27UQ that we have reviewed with Quantum Dot.
FALD (Full Array Local Dimming)
High Dynamic Range (HDR) is a very hot topic right now in the monitor market, with all the manufacturers rushing to try and offer support for HDR content in various ways. We won’t get in to the different specs and standards for HDR here, but we would recommend a review of our detailed HDR article for a lot more information on everything.
One very important aspect of HDR is achieving an improved dynamic range – improving the contrast ratio observed on the screen at any one time. A normal “static contrast ratio” for any LCD panel is limited by the panel technology being used, and it’s ability to bright and dark content at the same time. VA technology panels for instance have the strongest static contrast ratio currently (typically 3000 – 5000:1 in the specs) as they can display deep blacks at the same time as bright whites. IPS panels are limited to around 900 – 1300:1, and TN Film panels at around 900 – 1000:1 typically. HDR is all about trying to improve the contrast ratio observed from the screen and offer active contrast ratios in the tens of thousands (e.g. 50,000:1)
The way this is achieved is through the use of “local dimming”, where the screen is split in to zones and can be brightened or dimmed depending on the content being show in that zone. So it is possible to brighten the lighter areas of an image while simultaneously darkening the darker areas. An HDR display should always feature some kind of local dimming if you want to be able to achieve an improved dynamic range. Without it, you are restricted to the panels static contrast ratio and while there might be other HDR-related improvements in other areas like colour gamut, it’s not a “true” HDR display. This local dimming gives rise to significantly improved contrast ratios in practice and is the foundation for producing an HDR experience.
The effectiveness of this local dimming for LCD displays is directly linked to the number of zones the backlight can be divided in to. The more zones there are, the more control there is over the content being displayed. More cost effective local dimming solutions rely on a small number of zones (e.g. 8) where the backlight is positioned at the edges of the screen. They provide some HDR benefits and at least some form of local dimming, but don’t give much control over the variations across the screen’s content. The more preferred solution is to use a “Full Array Local Dimming” (FALD) backlight. With FALD, the screen is split in to far more zones, and each is directly lit by the LED backlight behind it. These are sometimes referred to as “direct lit” as opposed to “edge lit” displays. So far we have seen FALD backlights used on a couple of displays released or announced, with a 27″ model for instance currently having the ability to offer a 384-zone direct lit backlight. Future 35″ ultrawide screens will have a 512-zone FALD as well.
A FALD provides optimal control over the panel when it comes to local dimming and can produce the best HDR experience currently in the desktop monitor market. They can also allow very high peak brightness performance up to and above 1000 cd/m2 and when paired with wide gamut backlight options like Quantum Dot coating for instance, they can offer a true HDR performance. FALD however is very expensive and complicated to produce and so right now there are very few options available. Where they are available the displays are extremely expensive. There can be challenges getting the zones to respond fast enough to changes in content, especially when you consider they are being aimed at HDR gaming displays where sensitivity to the speed of changes is high. This is even harder when trying to combine the FALD with variable refresh rate technologies like NVIDIA G-sync, and one of the reasons why there was such long delays releasing models like the Asus ROG Swift PG27UQ and Acer Predator X27, the first FALD gaming displays release to market. Using FALD also adds considerably to the thickness and power draw of a display, and is very much in its early days of usage. If you want optimal HDR local dimming performance in the desktop monitor market right now, a FALD is the preferred option.