Author: Adam Simmons
Last updated: December 27th 2016
For many people in the modern world the humble computer is an integral part of their everyday lives. It has moved away from being the extravagant luxury of the lucky few to an essential component of most businesses and a welcome addition to many households. Despite the increasing miniaturisation of the computer and the adoption of novel portable forms such as the Tablet PC and integrated ‘all in ones’ the raw power and versatility of the desktop PC is still unmatched. One key feature of the modern desktop PC that distinguishes it from these prescribed and fairly inflexible alternatives is the inclusion of a base unit (often a tower) with components which can be readily upgraded. Another distinction is the common inclusion of a standalone monitor, with a matte or glossy screen, which has undergone the same ‘evolution’ of the rest of the PC – and will continue to do so.
Although the intricacies of different display technologies are often misrepresented by manufacturers and poorly understood by consumers there is one fundamental attribute that is commonly discussed; the screen surface. In contrast with what goes on ‘under the hood’, the screen surface is readily visible on the outside and embodies the essential visual connection between man (or woman) and monitor. Unlike the CRTs of the past, the modern display is not restricted by a hard and highly reflective glass surface. The nature of the screen surface is much more flexible and takes many forms – with varying degrees of anti-reflection or ‘glare busting’ properties. But as with most aspects of displays it is rarely that straightforward; there are certain caveats to the common ‘anti-glare’ surfaces. We explore the limitations of some of the more pervasive ‘anti-glare’ implementations and look at the alternatives and possible future direction of the computer screen surface.
A matte screen surface comprises an outer ‘polarising layer’ that has been coarsened using mechanical and sometimes additional chemical processing. The common methods of manufacture of this surface include multi-layered ‘spluttering’ or several passes of ‘dip coating’ optionally followed by chemical surface treatments. Although it isn’t necessary to explore the intricacies of these coating processes we will consider the desirable end-result of this processing. This is to achieve a matte finish to the screen surface which acts to diffuse ambient light rather than reflecting it directly back to the viewer; a smooth surface acts a bit more like a mirror. The vast reduction of unwanted reflection and glare gives rise to a term synonymous with such a screen; anti-glare. Although the diffusion of ambient light and hence reduction of glare is desirable, it isn’t an infallible solution. The optical properties of the surface work both ways – that is to say that light emitted from the monitor is also affected. Furthermore there is some degree of interference between the emitted light and the diffused incident light. The path of both emitted (from the monitor) and ambient (from the environment) light and its interaction with the matte screen surface is shown in the diagram below.
Whilst the desirable reduction in glare is achieved by the scattering of external light the image produced by the monitor is affected by the same diffusion process. The diffused ambient light also interferes slightly with the image produced by the monitor to exacerbate the process. The effects that this has on the image and the benefits attributed to the reduction of glare by a matte screen surface are summarised in the table below.
|Advantages of a Matte Screen||Disadvantages of a Matte Screen|
|Reduced glare improves visibility of image in areas of strong direct or ambient light
||Reduction in contrast and colour vibrancy
|Potential reduction in eyestrain in such circumstances as you don’t have to focus ‘through’ intense reflections or glare to see the image
||Slight to moderate reduction in sharpness – depending on thickness and layering of matte surface as well as monitor pixel pitch
|Dust, grease and dirt less visible||Generally more difficult to clean due to dirt penetration and relative difficulty seeing the fruits of your labour|
|Grainy or hazy texture apparent in some instances, particularly when displaying white and other light colours
Unlike the rough surface of a matte screen a glossy screen has a smooth outer polarising layer. Rather than diffusing ambient light this smooth surface tends to reflect it back quite directly, causing unwanted reflections and glare – particularly under strong direct light. On the flipside the light emitted from the monitor is unhindered by diffusion processes and reflections aside the image appears richer, more vibrant and unadulterated. Modern glossy polarising films are typically treated using an anti-reflective (AR) chemical coating such as magnesium fluoride or special polymers which act in part to aid absorption of some of the ambient light. Some of Samsung’s recent models have their screen surfaces laced with silver nanoparticles in what is dubbed an ‘Ultra Clear Panel’. This is designed to aid absorption of some ambient light to a slightly greater degree than a traditional anti-reflective chemical coating without impeding image performance.
The image below shows how the Ultra Clear Panel surface of a Samsung T27A950 and untreated glossy surface of a Dell Studio XPS15 laptop fairs on a fairly bright British summer’s day. The notion of British summer is not massively important in the context of this photograph, but it is to say it was nice and bright and even slightly sunny when the photographs were taken but dull and rainy shortly thereafter. Light is coming in from a window to the right of the monitor but no direct sunlight is striking the screen.
You can see in the image above that reflections are visible on both screen surfaces under such lighting conditions. The reflection is more intense on the Dell with a clear outline of the door, camera, cameraman’s hand and forearm and the red computer chair. On the Samsung these features are less well defined (obviously the chair is not visible at all as it is blocked by the laptop). Another observation is that the image on the Samsung appears richer whereas the image on the Dell appears bleached. Both screens were set to a brightness of 160 cd/m2 and under dark viewing conditions the Dell’s image does not appear bleached in this way – this is caused by the fairly strong ambient light and is something that the Samsung doesn’t suffer from in the same way. Anti-reflective surfaces commonly used on laptops include and sometimes on larger screens include; Dell TrueBright, ASUS ColorShine, HP BrightView and Sony Xbrite. These produce a darker image upon reflection than the untreated Dell.
Despite this slight reduction in reflections and darkening effect the Ultra Clear Panel is still very much a glossy surface. When displaying blacks and dark colours (or even light colours if ambient light is bright enough) reflections are still an issue and ambient lighting needs to be more carefully controlled. People may suggest that the brightness is turned up to help combat this, but the relative luminance of dark areas (particularly blacks) is considerably lower than bright areas regardless of the brightness setting. If it wasn’t clear from the mixed image above you will be under no illusion that this is anything other than a glossy screen surface when the monitor is switched off. This can be seen in the photograph below, which was again taken on a bright summer day. Note that the reflected image of the room on the Samsung is a little darker than on the Dell but objects still have distinct detail to them.
A minority of manufacturers (most notably Apple with their earlier ‘LED Cinema Display’ series) choose to forgo any anti-reflective treatment and include highly reflective untreated glass as the outermost surface. This is done largely for aesthetic reasons as there is no advantage of this over a properly treated anti-reflective surface when it comes to image quality. In general the amount of light reflected by any anti-reflective surface is reduced compared to an untreated glossy surface – whether using silver nanoparticles or chemical treatment.
Even though the reflection of ambient light can be reduced by the use of an anti-reflective coating it can never be completely eliminated, particularly where light is strong or the image is dark. If the monitor is set to a reasonable brightness, ambient light levels are relatively low and little light is falling directly onto the screen reflections should not be an issue. Because the light emitted takes a more direct path and isn’t diffused by a matte surface you are left with a ‘cleaner’ and more vibrant image which can be fully appreciated under such conditions.
The positive and negative attributes of a glossy anti-reflective screen surface are summarised in the table below.
|Advantages of an Anti-Reflective Screen||Disadvantages of an Anti-Reflective Screen|
|Reduced reflection in certain lighting conditions compared to an untreated glossy surface
||Strong ambient light levels and direct light falling onto the monitor can cause troublesome reflections and ‘bleaching’ of the image
|Easier cleaning due to lower dirt penetration and higher visibility of grease and dirt
||Potentially increased eyestrain due to difficulty focussing on image through reflections
|Generally greater aesthetic appeal -provided the screen is kept clean||Dust, grease and dirt more visible – especially when the monitor is switched off. Routine cleaning necessary|
|‘Cleaner’ image without hazing or graininess
|Direct light emission enhances contrast and image vibrancy
A half-way solution
Some manufacturers offer a compromise between the two – a surface type that is often dubbed ‘semi-glossy’. These surfaces are actually matte but are roughened up eithert a little or a lot less, giving them a smoother appearance and making the diffusion of light weaker. In other words; they have a relatively low haze value. Panel manufacturer AU Optronics uses such a surface on some of their modern VA panels, which have a haze value of 13-18% (considerably lower than the 25% typical on a BenQ 60Hz TN panel). This enhances the vibrancy and clarity of the image and greatly reduces the visible grain on white and light colours. It doesn’t quite bring the level of vibrant clarity or offer the same visual feel as a glossy monitor but certainly reduces the diffusion of emitted light and improves these characteristics compared to higher haze matte surfaces. The slight downside that follows this is that light from the environment that strikes the screen surfaces is also reduced less, increasing the glare slightly. Reflections are really a non-issue under most lighting conditions and things are certainly better in this department than a glossy screen surface. The image below shows the glare and reflective characteristics of a BenQ EW2420 with a low-haze matte surface (rear) compared to a Dell Studio XPS15 laptop with a TrueLife glossy screen surface (front). This photograph was taken on a bright day during late spring with sunlight streaming in through the window to the right.
You can see a clear and mirror-like reflection on the Dell laptop with the door, wall, chair and the laptop keyboard distinctly visible. On the BenQ you can see a fuzzy reflection of the door, the rear of the laptop and the cameraman’s hand. Once the screen is turned on this mild reflection ceases to be an issue. Direct light falling on the screen can still cause troublesome glare, but such viewing conditions are often problematic even for stronger matte screen surfaces. The image below shows the BenQ EW2420, under similar lighting conditions to the first photograph, displaying a mixed desktop background at 160 cd/m2. You can no longer see the reflected objects on the screen.
Samsung introduced a similar ‘very light matte’ (low-haze) screen surface to their SA850 series PLS (Plane to Line Switching) monitors and it has been used on more recent models as well, including some PLS and curved VA models. The surface makes use of a novel glass substrate processed to give a haze value of around 18%, which is considerably lower than the 24-28% typical on a Samsung TN panel monitor with matte screen surface. The screen surface texture is also smoother due to the process used. The end result is that the image and glare handling characteristics are some way between a ‘regular’ matte surface and a glossy surface. The image below compares the S27A850D (with a low-haze screen surface) to the Samsung 2030BW (regular matte screen surface) with both screens switched off. On the S27A850D you can see the outline of the windows facing the screen, whereas on the 2030BW you can see some slight glare at the periphery but no reflection. When the S27A850D is switched on to a reasonable brightness this generally isn’t an issue, as with the BenQ models.
A similar solution is used on some of LG’s AH-IPS panels, including 2560 x 1440 and 3440 x 1440 models. AUO’s AHVA panels (such as the BL2710PT and BL3201PT/PH) have an even lower haze value that sits quite close to that of their VA panels (13-16%). The clarity and relative smoothness of the image on these is excellent. Some models, most noteably from HP with their ‘Low Haze Enhancement’ treatment and various Philips models such as the BDM4350UC (below), use very low haze treatments typically around 1 – 5% haze. These provide an image that’s similar to a fully glossy solution, including giving that ‘wet look’ as ambient light strikes the surface, but with significantly reduced reflection. Note that the image below was taken in a bright room, but reflections appear quite soft. In somewhat dimmer conditions reflections that might remain bothersome on a ‘fully glossy’ screen are muted to the extent of becoming invisible and blending into the image.
It’s important to note that screen surface texture is also important and there are some models that buck the trends for ‘image smoothness’ expected from thier haze values. Good examples would be some 23.6 – 27″ IPS-type ‘4K’ UHD (3840 x 2160) panels such as those used on the Dell P2415Q or ASUS PG27AQ. These are light matte anti-glare (relatively low haze value), which preserves image vibrancy and clarity, but don’t have a particularly smooth surface texture. This is quite apparent when viewing lighter content, as it appears grainy. Some new ‘AD-PLS’ and ‘AH-IPS’ panels (including those with a 1920 x 1080 and 1920 x 1200 resolution) have relatively light-textured matte screen surfaces, even though the haze values (~25%) is shared by some models with noticably granier screen surfaces. LG’s 21:9 panels with 2560 x 1080 resolution have a similar haze value and an impressively smooth and ‘un-grainy’ surface texture.
Future screen surfaces
As explored in this article the reduction of glare and reflection on a monitor is a double-edged sword and must be finely balanced to avoid undesirable consequences. The ideal screen surface would be one which doesn’t interfere with light transmission, but at the same time is effective at reducing the impact of ambient light striking the screen surface. Back in 2003 optical film manufacturer MacDermid Autotype demonstrated a novel film coating that was intended to do just that. The film, which was co-developed with the Fraunhofer Institute of Solar Energy, was Dubbed Autoflex MARAG (MothEye AntiReflection AntiGlare). It was designed to mimic the tapered nanostructure of moth eyes (below) and the ability of these structures to maximise the harnessing of light with minimal reflection – as nocturnal moths need to operate in low light levels without light reflection on the eye surface giving away its position to predators.
The film would apparently offer excellent image clarity comparable to current anti-reflective (glossy) surfaces whilst combating glare from all external sources, including direct sunlight. It was claimed that the outer surface would reflect under 1% of light – which is very impressive indeed. According to our communications with MacDermid Autotype the research and development for this particular MARAG film has been completed and a limited range of portable devices were released which used the technology in 2009. Other companies have also applied similar principles to create their own ‘moth eye’ films. The most notable is the filter used on the Philips 46PFL9706H, which is a premium 46″ LCD TV. Unfortunately the MARAG process which is apparently more intricate than ‘moth eye’ surfaces from other manufacturers were not a commercial success, owing largely to the high development cost of even small areas of such a film. The process could be applied to films which were 800 x 600mm and would be suitable for use on PC monitors. However; developing a film of this size with high surface quality at a competitive price was not possible. As a result, the MARAG film itself was discontinued as of 2009 – but the company is working on a number of antireflective and low haze screen surfaces, using similar principles, which could be applied to monitors. Hopefully a good balance can be struck between price and performance when the film coatings are unveiled, all going well, during 2012 or 2013.
Another excellent innovation which could lend itself well to computer displays was recently unveiled by the Japanese company Nippon Electric Glass (NEG). The so-called ‘invisible glass’ consists of an extremely thin piece of glass coated on both sides with a highly efficient anti-reflective (AR) material. The material is layered with 30 ultra-thin film sheets, each sheet a few nanometres thick, and reportedly allows 99.8% light transmittance through the glass whilst reflecting a mere 0.1% of light on each side. This compares favourably to the 8% reflectance per side of a typical glass sheet and results in a piece of glass which, to all intents and purposes, appears invisible.
According to communication with NEG the technology is undergoing further refinement before any sort of commercial availability is considered. Currently the process is too expensive for even relatively small sheets to be considered economically viable, let alone larger sheets that could be used on a computer screen. Apparently such applications are being carefully considered and it is hoped that the layering process can be applied to something suitable to be used as a monitor polarising layer. Light transmittance through the coating is excellent and once the materials and processes are refined there should be real commercial interest in this coating.
We will certainly be keeping a keen eye on both of these technologies and their offshoots as well as other promising solutions. From our contact with panel manufacturers such as LG and Samsung, as well as Dell, it is clear that they are becoming acutely aware of user dissatisfaction with the two extremes of ‘matte’ and ‘glossy’. It is also clear that the cogs of innovation are turning and it is only a matter of time before this decision and subsequent compromises become relics of the past.