Mustek

White paper on the different TFT technologies:
General prior Introduction to Liquid Cristal technology.

Since the mid 80’s, the ramping Global requirement and market growth for Information technology created a huge general demand for Display monitors, those making the interface btw. the user and the IT system. From the early 80’s until the beginning of this century, CRT (i.e. Cathode Ray Tube) monitors largely dominated the market, while LCD (‘Liquid Crystal Display’) monitors, which first appeared around 1993, still were very much an object of prestige, emotion and proad ownership. CRT monitors used to come in very different quality standards and technical designs (from cheap and simple ‘Curved Dot Mask’ constructions to sophisticated ‘Flat Aperture Grille’ Diamondtron or Trinitron types) and in 3 main sizes: 17”, 19” and 21/22”.

However, because mainly of their bulk, they gradually lost their attractiveness to the public over the years, a phenomenon accentuated by their ever reducing price gap with 15”/17” LCD ‘Flat Displays’ monitors. Thus, the sale of TFT monitors eventually took over that of CRT’s, bringing a final blow to the ‘old’ Analog Technology all together. Over the recent years, multi billion $ investments were made in the global LCD panel production and the ever insatiable global demand for ever cheaper and bigger monitors brought the world monitor production to the verge of constant over supply of LCD displays with mostly similar specifications, features and price points. Their falling prices eventually allowed then to make their way into domestic households, and they finally became a mere standard domestic product along side the hoover and TV.

In this process, the initial fascination associated with the first ‘LCD flat displays’ back a few years ago vanished, and it gradually turned into a commodity product often summarized in a mere size/price ratio in the market. However, there are, more than ever, big and clearly visible quality differences between a cheap and a quality LCD monitor, be it in terms of picture quality, ergonomics, reliability and user features. The purpose of this paper is therefore to explore into details the issues that really matter and should be addressed when choosing an LCD monitor, starting with an explanation about the 3 main existing technical variations of the TFT panel technologies, in order to help monitor buyers making the right choice and finding the most adequate model for their needs.

This document is also intended to demystify the often deceiving technical data and claims made in product brochures, with mostly unverifiable foundation. It is in this respect rather paradoxical that nobody who wears glasses (i.e. the only other visual device used non stop many hours a day) seems prepared to make compromises on the optical quality of their designer spectacles, while the logics mostly applied to office or domestic LCD monitors (i.e. the ‘other’ full time optical device) is often that of sparing money only, in full disregard of any visual and ergonomic consideration. A very strange contrast of behaviors indeed.

Quality differences between PC monitors are indeed very noticeable when put side by side with a same content, regardless to any data sheet specification communicated by the manufacturer, and such a visual test remains by and large the only ‘proof of the pudding’ to compare them.

The main factors differentiating the quality of LCD monitors are:

1. The LC Panel matrixes
2. The electronics components that play a big role in the picture quality and the display reliability
3. The Ergonomic characteristics of the monitor
4. The product’s environmental friendliness and safety standards
5. The display features for the user

LC panel matrixes:
Explanation on the different existing LCD technologies used in displays.

Although ‘liquid crystals’ were first identified in 1888 by an Austrian Botanist (‘Friedrich Reinitzer’ 1855-1928) while he was investigating the properties of cholesterol in carrots, the first most major commercial break through came in 1970, when James Fergusson deposited a patent on Nematic Twisting, and subsequently sold it for commercial applications.

Liquid crytals are rod shaped molecules having a constant and repeatedly ordered atomic structure in normal ambient temperature (bellow melting points). The 2 remarkable characteristics and properties of such molecules in a so called ‘Nematic Phase’ are that they present the flowing properties of a liquid (i.e. without positional order) while having a long range orientational order.

These molecules also have an anisotropic (i.e. uni-axial) optical property like that of a crystal. Interestingly, these crystals orientate under the influence of a small voltage in the context of a display monitor, combining the benefits of a minimum power requirement to create active pictures and contents (by opposition of the CRT or Plasma technologies) , while being rugged and light enough to be transportable. There are mainly 2 basic types of LCD panels available to the industry: ‘passive’ (like in calculators. i.e. purely reflective), and ‘active’ matrixes.

For the purpose of Monitor displays, the latter is used, since only that type can achieve the necessary coloring, contrast and grey scaling qualities required to satisfy all modern IT applications. All active LCD displays share a same common functioning principle: a back light (usually a Cold Cathode Fluorescent Lamp or some Light Emitting Diodes) produces an isotropic (i.e multi directional) light source which passes through a ‘light diffuser’ (i.e. a film) that spreads the light uniformly without letting the CCFL tubes or LED’s diodes show through.

This uniform light then reaches and passes a first (back) polariser that orientates the light it in a set direction (light being directional). The millions of anisotropic crystals within the LC compound (contained within the 2 glass substrates) so transmit and guide this light wave further to a second (front) polariser (always placed perpendicularly to the first one), under the influence of 2 (minus and plus) electrodes.

Acting like millions of microscopic sections of optic cables tilting over in controlled directions under electrical influence, this still so far ‘white only’ light eventually reaches (or not.. depending on the voltage) a colour filter, which assigns a respective Red, Green and Blue coloring to each individual sub pixels. All sub pixel shine in 256 different intensities of green, red and blue light (in an 8 bit panel, corresponding to 2⁸), thus, by combination (i.e. 256x256x256), they offer a total of 16.7 Million colours. This dynamic colouring process works by colour addition (i.e. ‘additive system’) by opposition to printing (i.e. ‘substractive system’) whereby colours are substracted by superposition on paper. The chemical composition of the Liquid Crystal compound used in each display is specially optimized and adapted to each type of panel and of LCD technology.

To be able to fully understand the concept of quality when talking about LCD panels, one needs to explore and understand first the basic technical differences between TFT technologies. Most manufacturers of LCD displays do not communicate about the TFT technology they use in their displays (for obvious reasons), the domestic market not seem showing a huge interest for it neither so far.

This general lack of technical understanding about TFT allowed the common general misconception that all TFT monitors work according to one same unique principle and that they all offer a similar picture quality, which could be simply summarized in a couple of (creative) technical data such as ‘response time’ or ‘max contrast ratio’. However, these 3 types of TFT technologies do offer very fundamental visual quality differences, which again, only a side by side test can reveal objectively. This paper therefore aims at providing the necessary basic technical intelligence on TFT technology to anyone planning to purchase an LCD monitor in the future, in order to help making the right choice for one’s needs.

These 3 TFT technologies are typically:

1. Twisted Nematic (TN)

2. Vertical Alignment (VA)

3. In Plane Switching (IPS)
   

TN (Twisted Nematic)

This is the simplest and most commonly used LC technology, typically found in the vast majority of budget and consumer monitors, particularly those found in retail. Its design consists of 2 ITO’s (Indium Tin Oxide electrodes) per sub pixel (i.e. 1 for Red + 1 for Green + 1 for Blue) all 3 together forming one single pixel facing each other from each inner side of the glass substrate that contains the compound of liquid crystals. The millions of crystal cells contained between the 2 electrodes line up naturally in a twisted 90° structure when no voltage is applied between them (= Twisted Nematic Effect = ‘’always White on Off’’).

The surface of these 2 electrodes is treated with a polymer layer that is mechanically ‘rubbed’ (i.e. physically scratched) in perpendicular directions to one another, forming longitudinal slits in which liquid crystals anchor themselves in set directions at each end in a 90° twist, thus transmitting and guiding the light through to a second (front) polariser, in an ‘homogeneous’ alignment. The second polariser being always positioned perpendicularly to the back one, each sub pixel shines in different intensities as the light transmittance increases or decreases via polarisation, in accordance to the attack angle of the molecules against the second polariser.

When a small voltage is applied between the 2 electrodes (ITO’s), the long crystal molecules line themselves up into the direction of the current field (i.e. in the case of TN perpendicularly to both polarisers/glass substrates), breaking the naturally stacked and twisted order of the TN structure, gradually reducing its aperture ratio (i.e. light transmittance) to the front polariser.

TN panels are typically 6 bits only (for cost reasons), which does help a faster switching on the one hand, hence a shorter response time (=its main quality), but on detriment of colour performances altogether. With only 6 bits, TN panels can in principle reproduce the limited amount of 262000 colours (i.e. 64³). However, TN panels also come with ‘Frame Rate Convertors’ that algorithmically emulates these 6 bits into a pseudo 8 bits with 16.2 to 16.7 million colours, by dithering all neighbor pixels (i.e. switching them ON and OFF over different frame periods in a regular or repeating pattern) to create an alternating pigmentation which induces the vision of a particular target colour.

However, TN panels remain far from the visual qualities and performances of true genuine 8 bit panels in general, and of a VA or IPS type in particular (described later).

TFT panels are mass produced by the hundreds of thousands of units in China and Korea and their price fluctuates daily like semi conductors. Their cheapness and their lower design and manufacturing complexity come however at a big ranson: they offer the most restricted colour gamut of all 3 TFT technologies (i.e. range/depth of colours ) and achieve a rather miserable viewing angle with a very immediately pregnant colour shift (i.e. colours drifting with viewing angle), vertically even more than horizontally (= making this technology unsuitable for portrait applications).

Despite all the unrealistic technical claims often being made in data sheets, and despite the presence of optical films applied onto these matrixes that help opening their viewing angles, TN panels offer the poorest viewing angles of all 3 TFT technologies.

One must however concede that substantial quality improvements have been made on TN panels in recent times, and one can notice substantial differences in terms of colour depth and colour shift between TN panels of various manufacturers. Also, TN panels tend to offer a greater resistance to picture retention (i.e. remanence of static charges in the crystal material creating a ghosting effect in the picture) making them suitable for prolonged static applications such as touch screen applications.

As a nut shell, TN panels remain what they have always been: the cheapest but also the poorest visual alternative of the 3 TFT technologies. It is therefore not the interest of most popular manufacturers of budget monitors to communicate about these quality differences since most displays within their product portfolios feature TN panels.

Paradoxically, but logically, a new style and trend of communication started instead over the recent years praising new creative virtues of TN panels, backed up with unverifiable specifications to enhance the perceived quality of cheap displays. This practice seemed to make a hit on the average internet shopper, impressed by some impressive but deceiving technical data in relation to, typically, ‘Response Time’ or ‘Max Contrast Ratio’ (both of which are explained more into details bellow in separate sections).

NEC uses high quality TN panels in its Accusync, E and EA series, these models being destined to conventional office applications for which this LCD technology is certainly good enough and presents an interesting value for money. However, NEC tests, sources, test and purchases itself all the TFT panels it uses for its monitors, according to a stringent global procurement policy driven by quality, hence only the best quality matrixes make their way into NEC monitors, even at entry level.

VA (Vertical Alignment)

There are a few technical variations available of the VA LCD technology: namely MVA (=multi Domain Vertical Alignment) developed in 1998 by Fujitsu on one hand, PVA (patterned vertical alignment) from Samsung Electronics, and ASV from SHARP (the 2 latter ones patented early this century). While similar in functioning principle, they do differ on structural details.

Cheaper versions of MVA and PVA often come in 6 bits with dithering (i.e. Frame Rate Converters), while the best VA panels, such as the likes of AMVA or S-PVA for instance, do offer a true 8 bit colour depth performance for each RGB channel, hence a genuine combined 16:7 Million colours. The viewing quality, between VA panels is a lot more consistent than in TN panels.

In a VA panel, the liquid crystals naturally line up perpendicularly to the glass substrates, in a so called homeotropic state, i.e. without any twisted nematic effect. These crystals, having a negative dielectric, they typically rotate in an oblique direction to the voltage, i.e. in this case, in a parallel oreintation to the glass substrates. In its the absence, the picture remains black with a particularly efficient light obturation, what explains the usual high contrast ratio values typically associated to VA panels.

However, a precise molecular orientation cannot be obtained only on the back of sole material induction alone. It needs ‘physical’ help. In MVA panels, this help comes in the form of some physical arrangements made on the inner sides of the ITO’s and which are themselves placed in the inner sides of the substrates and in the from back and front electrodes which are shifted against one another.

In MVA (i.e. ‘Multiple Vertical Alignment), the ITO’s feature some tiny vertical triangular protrusions on their surface, which are off set between one another from back and front, and which slopes pre-define an inclination and switching direction for the molecules when a voltage higher than the switching threshold is being applied between them.

Each pixel is thus divided into (typically) 4 distinct cells (domains) in which molecules orientate along with the lateral electric fields provided by the shifted ITO’s, in split and oblique directions, spanned between the walls of each protrusion. As a result, the liquid crystals disperse in multiple directions, resulting in a wide viewing angle, while, while in off mode (i.e. Voltage bellow switching level), the molecules located on the flat portions of the substrate remain perpendicular to it and are not affected by the protrusions.

PVA (Paterned Vertically Aligned) panels, is another sophisticated technical alternative of the VA technology from Samsung. It does not use protrusions like in MVA to orientate the molecules in precise pre-determined angles, but relies instead on slits cut in the inner surface layer of the ITO’s, which are themselves also positioned off set, back and front, against one another. As a result, an arced and lateral electrical field forms up around the slits, that influences and determines the leaning angle of the liquid crystals in relation to the glass.

This arrangement results in a number of chevron shaped domains per sub pixel, addressing different viewing angles. In both cases, the electrical field is generated laterally through the LC compound when above switching voltage, while the LC material naturally keeps the crystals in a perpendicular alignment against the substrates when below that level.

Thus VA works in this respect on a contrary principle than in a TN panel but without Nematic effect. The other major difference being the reduced angle shifting of the molecules, granting this TFT technology with particularly fast switching times. In the case of S-PVA, a further major improvement of the viewing angle is obtained by differential driving of two sub pixel parts. Despite receiving the same nominal voltage, the two parts are driven with different voltage inductions by means of a separate capacity coupling, hence the leaning angle of the crystals located within the domains located within that second field point in a different direction than the other one, so opening even further again the viewing angle and the light dispersion of this technology.

The leaning angle of the molecules against the substrate in a VA panel keeps however changing constantly given its very functioning principle, like in a TN panel, which explains the noticeable colour dependence on viewing angles, particularly noticeable with light colour tones.

However, because the fanning out of the millions of anisotropic molecules in different directions, VA offers a drastic general improvement regarding colour shift, compared with TN.

As seen earlier, since this technology can also block off light efficiently, it offers a particularly deep black state, a bright white, thus, de facto, a very high contrast ratio. It is also characterized by a vibrant and fully saturated (if not necessarily realistic) colour rendition, particularly when all sub pixels are opened at full gain (i.e. when the crystals are fully tilted in an oblique direction to the polyrisers, as in, similarly to the alignment direction of an IPS panel), translating into very intense Red, Green and Blue pixels that remain colour consistent regardless in this case of the viewing angle.

In that respect, the VA technology, while representing a massive improvement over the limited colour reproduction performances of TN, cannot quite rival IPS for colour management applications, where the neutrality, realism and consistency of colours is paramount to the graphic designer, regardless to any directions .

For all these reasons , MVA and PVA panels represent a very good compromise indeed with a wide viewing angle, very high contrast, acceptable colour gamut, fast response time, and a characteristically deep black and bright white level. However, despite their impressive colour rendition, VA monitors do not quite rival the neutral and balanced colour reproduction of IPS.

NEC typically uses such TFT panels in monitors destined to Cad/Cam and industrial 3D applications (i.e. ‘Autocad’) where the full colour saturation and contrast characteristics of VA comes as an advantage for the critical professional users needing fine, visible and highly contrasted details. This technology is therefore typically to be found in 19”std to 24”wide NEC models, exclusively in quality 8 bits S-PVA versions.

IPS (In Plane Switching)

IPS is the TFT technology that offers the most realistic and neutral colour rendition, but it comes at a higher price than VA, and particularly than TN.

IPS was initially developed by Hitachi in 1996 as a vastly superior technical alternative to TN panels, and has been constantly further improved over the years, As far as desk top IT monitors are concerned, mainly 3 manufacturers are active in the production of High End IPS panels: Hitachi / LG / and NEC (NPL). The functioning principle of IPS is intrinsically different from that of TN or VA. While the two latter shoot a back to front switching voltage between 2 electrodes placed on each inner side of the glass substrates, IPS stacks all crystals in one single ‘plane’ structure that pivots on its own axis under the influence of a voltage generated between 2 rubbed electrodes placed side by side on the back substrate, and which also feature in some case some kind of ‘domained’ structure on their surface, in which the crystals located on each end of the plane structure anchor themselves, holding the plane of molecules from each extremity.

The section of the plane of molecules located between the electrodes and thus coming under electrical influence, rotates on its own axis when a voltage above switching level is applied. Because of this unique functioning principle, the liquid crystals in an IPS panel consistently line up parallel to the glass + polarisers at all time, regardless to the grey scales they are to reproduce and to their input gain, while the lower viscosity of the IPS LC material (compared to the other TFT technologies) compensates for a physically lower switching process (which can be remarkably improved by overdriving but at the expense of focus). Since this TFT technology uses the full length of the crystals to convey the light to the front polariser, it radiates and disperses the viewing angle consistently in all directions without any sign of colour shifting whatsoever, regardless to its tone or grey scale, and even regardless to the vertical of horizontal axis. For this very reason, IPS offers, by far the widest viewing angle and colour depth of all TFT technologies.

However, the presence of two electrodes per sub pixel at the back of the panel (instead of super positioned or shifted ones in the case of TN and VA), physically blocks off more light, thus it limits the aperture ratio (=overall panel transmittance).

To compensate this, IPS panels typically need stronger back lights than their TN and VA siblings, thus, they usually have a higher calorific generation which is usually tactilely noticeable.

The second most spectacular characteristic of IPS remains however its impressive deep colour Gamut (=range of colours). As a comparison, while TN panels typically achieve up to a maximum of 72% of the ADOBE RGB Gamut, IPS panels typically achieve well over 100% ‘out of the box’ (i.e. H-IPS), even reaching 109% of it in the case of the NEC SpectraView Reference 21 model featuring a dynamic RGB LED back light model and an a very high performance colour filter. This characteristic obviously pre-destines IPS to colour and photo applications where the depth, accuracy of and realism of colour reproduction are key, and where the extra gamut reveals the additional details and colour nuances normally compressed in the case of TN and VA technologies.

IPS thus offers a true colour veracity and a fine Gama reproduction (more natural and closer to the more natural reproduction of the of the old CRT monitors), with, as an example, human flesh looking truly ‘human’ by opposition to the typical ‘crustacean reproduction’ of some entry level LCD monitors.

IPS is also characterized by a total absence of horizontal or vertical colour shift (by opposition to TN and VA). A simple side by side comparison between the 3 TFT technologies will immediately provides evidence of this phenomenon. It is therefore not surprising that IPS is the prime choice for colour management applications requiring colour finesse, accuracy, depth and neutrality.

However, there are also down sides to IPS. First, its price range (typically 25% to 50% higher than TN for a same monitor size) restricts it to professional applications. IPS is indeed a lot costlier to manufacture than the other 2 technologies, plus, it cannot rely on the same sort of economies of scales as the popular TN panels enjoy to amortize the investment made in development and production, The few Because of its target applications, IPS is therefore nowadays only available in larger 16:10 sizes, typically 24”, 26” and 30”.

A new generation of IPS panels (e-IPS) is however to see the light soon in the form new 21.5” (16:9) 23” (16:9) and 27” (16:9) with full HD resolution. e-IPS relies on a design optimization of its ITO’s to drastically increase the aperture ratio (already doubled over the original IPS design in its latest H-IPS version), thus a downsizing and saving on components and back lights can be made, bringing its cost more in line with current market price expectations, and rendering this technology available to a wider target audience.

The second main weakness of IPS is its ‘light leakage’ on fully black pictures, due to its superior light dispersion performance, IPS also tends to transmit negligible amounts of light to the front polyriser, even when of voltage remains bellow switching levels (= when the picture is fully black). Hence, its black level is no match for the exceptional low black level of, say, PVA.

Nevertheless, the very latest developments made in IPS technology (i.e. between the initial IPS panels and the very latest H-IPS generations) bring its black performance ever closer to it. For all these reasons, although it offers a vastly superior colour rendition and finesse of grey scaling than the other 2 TFT technologies, IPS paradoxically quotes arithmetically lower typical Max Contrast values than the 2 other TFT technologies.

The light leakage phenomenon of IPS is however only noticeable in pitch black rooms, where some light purple/green stitches can appeare on full black pictures viewed at extreme viewing angles or on picture rand.

However, apart for nocturne Gaming applications, this phenomenon immediately becomes quickly completely irrelevant in normal ambient light environments and will never inconvenience any graphic designer or digital retoucher for whom this technology is primarily pre-destined. Finally, as mentioned previously, IPS usually quotes a slower nominal response time specifications than TN or VA (although it was reduced to a more than sufficient 6ms in the mean time with overdriving), but one needs to understand that the balanced nature of its ‘rise and fall’ curve (i.e. white-black-white), compensates largely for it slower switching characteristics and it visually matches the claimed faster other 2 TFT technologies. Finally, IPS is more sensitive to picture retention than TN ro VA. Thus it would not be a prime choice for long term static applications such as ‘touch screen’ for instance.

NEC is one of the very last premium brands to produce and use IPS panels for its high end monitors. NEC being a solution oriented manufacturer of professional LC desktop displays, it designs and manufactures monitors to specific and critical professional requirements.

Typically, IPS panels are implemented in monitors destined to Graphic designers and Colour professionals in the photo retouching or the pre-press industry. It is also favored by grey scale sensitive radiologists having to make life depending diagnosyses on DICOM calibrated medical monitors. IPS panels excel indeed at reproducing very fine and necessary nuances and shades of grey and they offer a very neutral accuracy, which is required for such critical applications.

For the same reasons, NEC SpectraView monitors (high end colour management models) exclusively feature state of the art IPS panels, for they represent the most credible colour reproduction, and come as the natural successor to defunct CRT monitors that were long praised by graphic designers for their colour neutrality and realism. The NEC daughter company NLT, is a producer of IPS panels (SA-SFT), which to be found in models such as the 2190UXi and SpectraView 21.

Appendices to explanations on the different TFT technologies :

Explanations about Response Time:

The recent fashion consisting of publisizing ever smaller ‘Response Time’ data in LCD data sheets was mainly motivated by the new public fascination for gaming and for down load videos, requiring image fluidity to improve their enjoyment.

It is true that early this century, LCD panels were characteristically suffering of a poorer video rendition than CRT or Plasma displays. Initially, a TÜV standard was used, that encompassed the Rise and the Fall of an LCD panel from Black to White and reverse (-10% top and bottom), was used to measure the response time, summed up in milli-seconds.

However, physically speaking, small gradations of grey (i.e. small nematic changes in a TN panel) are obtained with substantially lower driving voltages than for the full black/white spectrum changes, thus, paradoxically, the response time actually became a lot slower, within the mid range of grey scales where videos take place. Therefore some consumer oriented brands started launching simplistic marketing messages to the market such as ‘the smaller the response time the better the monitor’, and were quickly trapped in their own game, forced to continuously undercut the response time specifications of each new model, down to the stage where TÜV measurements methods could enable them to go any lower. They then resorted to creating their own interpretation of the measurement of switching time, by creating so called ‘Grey to Grey’ measurement, without any existing clear definition nor explanation of it, hence removing any relevance of this data, and artificially increasing the impressiveness of this data to two milli-seconds in their product brochures.

For reference, it has been physiologically proven that under 8 milli seconds, few people could actually spot differences in video fluidity on an LCD display. It is also surprising that such deceiving practices be tolerated in the market without any legal consequences, which goes to show the general complaisance in the trade about constantly communicating the highest possible specifications to the user, to sell easier and to influence a prospect into buying what are in essence often mediocre budget TN monitors.

However, the technical artifact consisting of applying the same voltage for small gradations of grey as for full Black/White spectrum changes (= so called ‘overdrives’) does indeed bring significant improvements to the video performance on TFT displays, it also tend to deteriorate their focus (=‘overshooting’, i.e. shadowing behind letters) while some potential damages on the long term can appear in the form of picture ghosting. In this respect, switchable chassis overdrives (like in NEC 90’s series monitors) should be preferred to monitor designs featuring panel overdrives which are constantly on.

Explanation about Contrast Ratio

Contrast ratio is the division the Max Candelar brightness of the monitor by the lowest level of black. Therefore, by pure arythmetics, the higher the top value (hence top brightness of a monitor), the lower the denominator and the higher the contrast ratio. The lowest black value of the panel is highly influenced by the ambient light environment since it presents reflective characteristics too. Hence to obtain a lowest possible depth of black, contrast ratio measurements are made exclusively in pitch black (photo type) rooms in the complete absence of ambient reflective light, conditions that do not exist elsewhere. The wide spread use of adaptive back light technology (or so called ‘dynamic’ back light) further increases the contrast ratio of LCD monitors by diming the back light by voltage reduction. A sensor detects when the picture gets dark and automatically lowers the back light by a few decimals of candela, exponentially increasing the contrast ratio to impressive top arithmetic values, i.e. 300:0,1c= 3000:1. However one needs to understand that put back in normal ambient conditions, the denominator increases accordingly to say 0,5c, thus the contrast ratio for the same monitor becomes 600:1, values which are a lot more realistic and relevant to the regular office user.

Such measurement methods have been largely abused by monitor manufacturers, mostly those of entry models with TN panels, to quote ever higher max contrast values, associating a high contrast ratio with monitor quality, while in real life it only has a minor influence on the overall visual quality or ergonomics of a monitor. Again, marketing plays unfortunately a big part in the general product intelligence of the public, whereby, only side by side test can prove reliably conclusive.