TFT Central

LCD stands for "Liquid Crystal Display" and TFT stands for "Thin Film Transistor". These two terms are used commonly but refer to the same technology. Often the TFT terminology is used more when describing desktop displays, whereas LCD is more commonly used when describing TV sets.

Screen Size

As TFT screens are measured differently to CRT monitors, the quoted screen size is actually the full viewable size, measured diagonally. Roughly as a guide:

Obviously these are not always exact, but it is a good rough guide to the sizes. For instance a 19” CRT may offer a viewable area of more like 18”. Nowadays, 15” TFT’s are fairly rare and even 17" screens are beginning to disappear. The 19” and 20" models are increasingly affordable and the majority of the technological advances have shifted to these larger screen sizes. 22" - 24" and larger screens are now becoming the focus of manufacturers as we move away from a single use desktop screen, and into a multi purpose monitor. While there is still some minimal concentration on the 19" market, the focus has shifted to Widescreen format monitors, in the 19" - 30" ranges.

Resolution

The resolution of a TFT is an important thing to consider. All TFT’s have a certain number of pixels making up their liquid crystal matrix, and so each TFT has a “native resolution” which matches this number. It is always advisable to run the TFT at its native resolution as this is what it is designed to run at and the image does not need to be stretched across the pixels. This helps keep the image at its most clear and at optimum sharpness. Some screens are better than others at running below the native resolution (see the interpolation section). You cannot run a TFT at a resolution of above its native resolution. Make sure your graphics card can support the desired resolution of the screen you are choosing, and based on your uses. If you are a gamer, you may want to consider whether your graphics card can support the resolutions you will want to use to power your screen.

Screen Size (diagonal inches)	Common Resolution	Other Resolutions Available (different aspect ratio)
15	1024 x 768
17	1280 x 1024
17 WS	1280 x 768
18	1280 x 1024
18.5 WS	1366 x 768
19	1280 x 1024
19 WS	1440 x 900
20	1600 x 1200
20 WS	1680 x 1050
21	1600 x 1200
21 WS	1680 x 1050
21.5 WS	1920 x 1080
21.6 WS	1920 x 1080
22 WS	1680 x 1050	1920 x 1200
23 WS	1920 x 1200	2048 x 1152
23.6 WS	1920 x 1080
24 WS	1920 x 1200	1920 x 1080
25 WS	1920 x 1080
26 WS	1920 x 1200
27 WS	1920 x 1200	1920 x 1080 2048 x 1152
28 WS	1920 x 1200
30 WS	2560 x 1600

More and more you will see resolutions referred to by their common HD equivalents. HD content is based purely on an improved resolution of the source and is defined by the vertical number of pixels in the resolution. i.e. a 720 HD source has 720 vertical pixels in it's resolution and a 1080 will have 1080. On top of this, there are two ways of showing this content, either using a progressive scan (e.g. 1080p) or an interlaced scan (1080i)

To display this content of this type, your screen needs to be able to 1) handle the full resolution naturally within its native resolution, and 2) be able to handle either the progressive scan or interlaced signal over whatever interface you are using. If the screen cannot support the full resolution, the image can still be shown but it will be scaled down by the hardware and you won't be take full advantage of the high resolution content.

So for a monitor, if you want to watch 1080 HD content you will need a monitor which can support a vertical resolution of 1080 pixels, e.g. a 1920 x 1080 monitor.

Panel Type

There are a few main types of panel technology widely used in the TFT market. Their implementation is dependent on the panel size mostly as they vary in production costs and in performance.

TN film (Twisted Nematic + Film) panels where the first panels to be used and are still widely implemented in many TFT’s today, especially mid to low end screens. This is due to the low manufacturing costs of TN panels. Traditionally they were not always very good at displaying blacks, but modern TN Film panels are actually very good in this regard. In fact many can compete with even VA matrices. There is also a problem with pixels dying and becoming a bright colour rather than just completely going out (black). The main issue with TN Film panels is that they have restrictive viewing angles of up to a realistic range of about 140 horizontally. Vertical viewing angles are very poor generally and suffer from a characteristic blackening of the image as you look from below. TN film panel traditionally offer the fastest pixel response times, and with the implementation of RTC / overdrive technologies, the grey to grey transitions have become even faster. Today, TN Film panels are used in the majority of gamer-orientated screens and are often used to break into new screen sizes, offering a cost effective way to provide larger screens without increasing the price too much. For more information, see our detailed panel technologies guide.

IPS (In Plane Switching) was introduced to try and improve on some of the drawbacks of TN Film. It was developed by Hitachi and was dubbed “super TFT”. They improved on viewing angles up to about 170H. This was done by controlling liquid crystal alignment slightly differently, but unfortunately, can affect response rate of the pixels. As such they are not as good for gaming as TN panels. IPS panels were later developed into Super-IPS (S-IPS) panels by their main manufaturer now, LG.Display (formerly LG.Philips). Production costs were lowered which has meant they have become more widely used. S-IPS offer perhaps the most accurate colour reproduction available in the TFT panel market, and the widest viewing angles as well. They are also free of the off-centre cotnrast shift which is evident on VA matrices, and as such are commonly the choice of graphics and colour professional displays. Response times were traditionally behind those of TN Film and VA panel variants, but modern IPS panels using response time compensation (RTC) including the new generation of Horizontal IPS (H-IPS), Enhanced S-IPS and Advanced Super IPS (AS-IPS) panels can offer responsiveness to rival both. For more information, see our detailed panel technologies guide.

VA (Vertical Alignment) panels are the third type used in modern TFT’s. The early VA panels have been scrapped due to poor viewing angles, and in their place came the Multi-Domain Vertical Alignment (MVA) and Patterned Vertical Alignment (PVA) panels. These offer superior colour reproduction compared with TN film, but not quite as good as IPS / S-IPS. They do however have the advantage of being able to show good black levels and viewing angles are also very good. There is a characteristic off-centre contrast shift detectable from VA matrices, but not everyone will notice this or find it a problem. The wide viewing angles are achieved by having all the colour elements of the panel split into cells or zones. These are formed by ridges on an internal surface of filters. The purpose of this design is to enable liquid crystals to move in opposite direction to their neighbours. It allows the observer to see the same shade of colour irrespective of a viewing angle. There have been improvements to the MVA and PVA technologies, which has given birth to the Premium-MVA (P-MVA), Super-MVA (S-MVA), Advanced-MVA (AMVA), Super-PVA (S-PVA) and cPVA technologies. One of the main improvement in recent times has been in responsiveness, with overdrive playing a key role. For more information, see our detailed panel technologies guide.

Advanced Super View (ASV) - This technology was developed by Sharp for use in some of their TFT displays. It consists of several improvements that Sharp claim to have made, mainly to counter the drawbacks of the popular TN Film technology.

They have introduced an Anti-Glare / Anti-Reflection (AGAR) screen coating which forms a quarter-wavelength filter. Incident light is reflected back from front and rear surfaces 180° out of phase, thus canceling reflection rather diffusing it as others do. As well as reducing glare and reflection from the screen, this is marketed as being able to offer deeper black levels. Sharp also claim to offer better contrast ratios than any competing technology (VA and IPS); but with more emphasis on improving these other technologies, this is probably not the case with more modern panels.

Ultra Wide Viewing Angles - Offering wide viewing angles of at least 170 in all directions. This is like VA and IPS technologies do, but Sharp claim that this doesn't impact response time as much as other technologies do. This is achieved thanks to a specially designed cell structure, which supposedly offers blur free images on moving video. It is interesting to note that Sharp's description of this technology doesn't mention gaming, only that fast moving movies are fine with their ASV displays. There are very few ASV monitors around really, with the majority of the market being dominated by TN, VA and IPS panels.

Advanced Fringe Field Switching (AFFS) - This technology was developed by BOE Hydis, and is not really very widely used in the desktop TFT market, more in the mobile and tablet sections. It is worth mentioning however in case you come across displays using this technology. It was developed by BOE Hydis to offer improved brightness and viewing angles to their display panels and claims to be able to offer a full 180 / 180 viewing angle field as well as improved colours. This is basically just an advancements from IPS and is still based on In Plane technology. They claim to "modify pixels" to improve response times and viewing angles thanks to improved alignment. They have also optimised the use of the electrode surface (fringe field effect), removed shadowed are between pixels, horizontally aligned electric fields and replaced metal electrodes with transparent ones. More information about AFFS can be found here.

This panel technology was developed by NEC LCD, and is reported to offer wide viewing angles, fast response times, high luminance, wide colour gamut and high definition resolutions. Of course, there is a lot of marketing speak in here, and the technology is not widely employed in the mainstream monitor market. Wide viewing angles are possible thanks to the horizontal alignment of liquid crystals when electrically charged. This alignment also helps keep response times low, particularly in grey to grey transitions. Their SFT range also offers high definition resolutions and are commonly used in medical displays where extra fine detail is required.

NEC's SFT technology was first developed to be labelled as Advanced-SFT (A-SFT) which offered enhanced luminance figures. This then developed further to Super Advanced-SFT (SA-SFT) where colour gamut reached 72% of the NTSC colour space, and then to Ultra Advanced-SFT (UA-SFT) where the gamut was still at 72% or higher, but with a further enhancement of the luminance as compared with SA-SFT. These changes were all made possible thanks to the improved transmissivity of the SFT technology.

Response Time

Response Time is the spec which many people, especially gamers, have come to regard as the most important. It's official measurement refers to the time taken for a pixel to change from being black (off) to white (on) and then back to black. In practical terms, it refers to the speed of the pixels and how quickly they can change from one colour to another, and therefore how fast the picture can be redrawn. The faster this transition can change, the better, and with more fluid changes the images can change overall a lot faster. This helps reduce the effects of blurring / ghosting in games and movies which can result if response time is too slow. Generally, the lower the response time, the better.

Do not rely entirely on response time specs quoted by manufacturers as a be all and end all to the monitor’s performance. Different manufacturers have different ways of measuring their response time, and one 5ms panel might not be the same in real use to another 5ms panel for instance. Panel technology also plays a part here, and don't get confused with standard response times and grey to grey figures. However, response times can be treated a guide to the performance of the screen, and as a rule of thumb, the lower the better.

Response Time In More Detail

Response time is measured as the rise time (tR) and fall time (tF) of a pixel as it changes black > white > black. This is effectively the time it takes to change a pixel from one colour to another and the total ‘response time’ is quoted as the total of the tR + tF. Be wary of the figures manufacturers quote, as sometimes the ‘response time’ can be quoted as just the rise time, and not the total response time.

In reality the response time of the pixels will vary depending on the colour change they are making. In practice, a full black > white change is not common, and instead the pixel transitions are in shades of grey, and are then passed through the colour filters. The speed of changes will depend on the darkness of the transition, and traditionally (before overdrive) the transitions to lighter greys will be faster. Therefore, a manufacturers quoted response time does not necessarily mean that the speed of the pixels is the same for all the transitions. It is always a good idea to see if there are any third party measurements of response time for any given screen, by places like Tom’s Hardware Guide and X-Bit Labs before considering how fast a panel really is in practice. Also take into account perceived response time measurements and comparisons between screens as we carry out in our reviews.

Take for instance this example response time graph I have put together. The X-axis ranges from code 0 to code 255, and the Y-axis shows the response time across this range. As you progress to the right of the graph, the transitions are getting progressively lighter. So for instance at code 100 the transition is from black > dark grey, but at code 200 the transition is from black > light grey. At code 255, this is the change from black > white and is traditionally the fastest transition because this is the widest change and therefore the largest voltage is applied to the liquid crystals. For many years, manufacturers have quoted the fastest transition of the panel as the figure for ‘response time’. This was always at the black > white transition and so this became accepted as the ISO standard norm for measuring response time. If this graph were a real panel, it would very likely be quoted as a 10ms screen and shows a characteristic curve for a traditional, non-overdrive, TN Film panel.

As you can see from the graph, the actual response time can vary quite considerably across the whole grey range, with some changes being much slower. This is the reason you cannot always rely on quoted specs to give an accurate representation of a TFT’s actual pixel response performance. The quoted figures from manufacturers should be treated as a rough guide however to a panels response time, as generally there has been some improvements in the overall latency with the changes from 25ms > 16ms > 12ms > 8ms > 5ms panels for instance. The shape of the graph is likely to remain quite similar, but overall, the curve will probably be a little lower when comparing an 8ms to a 16ms for instance.

Response Times and Different Panel Technologies

One thing to note regarding pixel response time is that the overall performance of the TFT will also depend on the technology of the panel used. TN film panels offer response time graphs similar to that above, but screens based on traditional VA / IPS variant panels can show response time graphs more like this:

This is again a mock up, but shows a typical curve shape you may expect from a VA / IPS panel (not using overdrive) when compared with TN film. Although a VA/IPS screen might be quoted as perhaps 12ms for instance, this might not mean it is as reactive as a 12ms TN film panel. Again, it is a good idea to check for reviews which measure the response time across the whole range.

Response Time Changes and the Introduction of Overdrive

With the introduction of overdrive panels the ISO point is not always the fastest transition any more, and so if a monitor has a response time quoted as “grey to grey / G2G” then you can be pretty certain it is using overdrive technology. The manufacturers still want to quote the fastest response time of their panel and show the improvements they have made though, but be wary of this change away from the ISO standard of quoting response times. The ISO response times have hit a wall really with TN Film stuck at 5 - 8ms, IPS stuck at around 16ms and MVA/PVA stuck at about 12ms. However, with the introduction of overdrive technologies, the more important grey transitions are now significantly improved, and response times of 2 - 5ms G2G are now common place.

Please see the following section regarding the technologies introduced with overdrive to help improve response times: < more info >

Some sites like Tom's Hardware and X-Bit Labs have access to advanced photosensor (photodiodе + low-noise operational amplifier) equipment which allows them to measure response time as detailed above. Graphs showing response time according to their equipment are produced. Other sites like ours for instance prefer to rely on observed responsiveness to compare how well a panel can perform. I think it is important to study both methods if possible to give a fuller picture of a panels performance. TFT Central and other places like BeHardware have often used a program called Pixperan (developed by Prad.de) which is good for comparing monitor responsiveness with its series of tests. The favourite seems to be the flag test as shown here:

Movement isn’t perfectly fluid. Depending on its speed, the car is shown in several successive positions. If the car goes very fast, the positions are very close and the eye perceives a flowing movement. A monitor without ghosting effects would have previous images completely fading away when a new one appears. This is the theory and in practice, it´s often not the case as images fade progressively. Sometimes up to 5 afterglow images remain on the monitor and represent the visible white trail behind objects. Some monitors have strong overdrives in addition to image anticipation algorithms. In this case, an image can appear in front of the main object, creating a white halo in front of objects in motion.

Contrast Ratio

The Contrast Ratio of a TFT is the difference between the darkest black and the brightest white. As a rule of thumb, the higher the contrast ratio, the better. The depth of blacks and the brightness of the whites are better with a higher contrast ratio. When considering a TFT monitor, a contrast ratio of 700:1 to 1000:1 is pretty standard nowadays, but there are models which boast specs up to over 1000:1. Be wary of quoted specs however, as sometimes they can be exaggerated. VA panel specs are generally the most reliable and accurate to reality when considering contrast ratio. Some technologies boast the ability to dynamically control contrast and offer much higher contrast ratios of well over 3000:1. Be wary of these specs as they are dynamic only, and the technology is not always very useful in practice. Traditionally, TFT monitors were said to offer poor black depth, but with the extended use of VA panels, the improvements from IPS and TN Film technology, and new Dynamic Contrast Control technologies, we are seeing good improvements in this area.

Brightness

Brightness is a measure of the brightest white the TFT can display. Typically TFT’s are far too bright for comfortable use, and the On Screen Display (OSD) is used to turn the brightness setting down. Brightness is measure in cd/m² (candella per metre squared). Note that the recommended brightness setting for a TFT screen in normal lighting conditions is 120 cd/m²

Colour Depth

The colour depth of a TFT monitor is related to how many colours it can produce and should not be confused with colour space (gamut). The more colours available, the better the colour range can potentially be. Colour reproduction is also different however as this related to how reliably produced the colours are compared with those desired.

Panel Colour Depth	Total Bits Per Colour	Steps Per Sub pixel	Total Colours
6-bit	18-bit	64	262,144
6-bit + FRC	-	-	16.2 million
8-bit	24-bit	256	16.7 million
10-bit	30-bit	1024	1.07 billion

The colour depth of a panel is determined really by the number of posible orientations of each sub pixel (red, blue and green). These different orientations basically determine the different shade of grey (or colours when filtered in the specific way via RGB sub pixels) and the more "steps" between each shade, the more possible colours the panel can display.

At the lower end, TN Film panels are quite economical, and their sub pixels only have 64 possible orientations each, giving rise to a true colour depth of only 262,144 (i.e. 64 steps on each RGB = 64 x 64 x 64 = 18). This is also referred to commonly s 18-bit colour (i.e. 6 bits per RGB sub pixel = 6 + 6 + 6) This colour depth is pretty limited and so in order to reach 16 million colours and above, panel manufacturers commonly use two technologies: Dithering and Frame Rate Control (FRC). These terms are often interchanged, but strictly can mean different things. These technologies simulate other colours allowing the colour depth to improve to typically 16.2 million colours.

Other panel technologies however can offer more possible pixel orientation and therefore more steps between each shade. VA and IPS panels are traditionally capable of 256 steps for each RGB sub pixel, allowing for a possible 16.7 million colours (true, without FRC). These are referred to as 8-bit panels with 24-bit colour (8-bit per sub pixel = 8 + 8 + 8 = 24). However, some time ago it seemed that some VA and IPS panels perhaps offer only a 6-Bit colour depth and use other methods to boost the colour palette. Official information is scarce, but this article covers the situation in more detail if you're interested. On the most part though, it can be considered that VA and IPS panels can offer an 8-bit colour depth.

10-bit colour depth is typically only used for very high end graphics uses, but a 10-bit panel is capable of a true 1024 shades per sub pixel. This allows for a massive 1.07 billion colours and a 30-bit (10-bit per sub pixel = 10 + 10 +10 = 30) colour depth. These are currently only available in some high end IPS (often referred to as p-IPS) panels. In theory, the more steps per sub pixel, the more detail can be shown and this is important where gradients are common or subtle differences need to be seen. For a 10-bit panel to be truly utilised, you need an entire 10-bit "journey" though. See here for further information.

Experiments at the beginning of the last century into the human eye eventually led to the creation of a system that encompassed all the range of colors our eyes can perceive. Its graphical representation is called a CIE diagram as shown in the image above. All the colors perceived by the eye are within the colored area. The borderline of this area is made up of pure, monochromatic colors. The interior corresponds to non-monochromic colors, up to white which is marked with a white dot. 'White Colour' is actually a subjective notion for the eye as we can perceive different colors as white depending on the conditions. The white dot in the CIE diagram is the so-called flat spectrum dot with coordinates of x=y=1/3. Under ordinary conditions, this color looks very cold, bluish.

If we had three sources of different colours the question is which other colours can be made by mixing the sources? If you mark points with the coordinates of the basic colors in the CIE diagram, everything you can get by mixing them up is within the triangle you can draw by connecting the points. This triangle is referred to as a color gamut.

Laser Displays are capable of producing the biggest color gamut for a system with three basic colors, but even a laser display cannot reproduce all the colors the human eye can see, although it is quite close to doing that. However, in today's monitors, both CRT and LCD (except for some models I’ll discuss below), the spectrum of each of the basic colors is far from monochromatic. In the terms of the CIE diagram it means that the vertexes of the triangle are shifted from the border of the diagram towards its center.

Traditionally, LCD monitors were only capable of covering the sRGB colour space as shown in the diagram above, if that. This is due to the backlighting used in these displays. Cold-cathode fluorescent lamps (CCFL) that are employed in them emit radiation in the ultraviolet range which is transformed into white color with the phosphors on the lamp’s walls. These backlight lamps shine through the LCD panel, and through the RGB sub-pixels which act as filters for each of the colours. Each filter cuts a portion of spectrum, corresponding to its pass-band, out of the lamp’s light. This portion must be as narrow as possible to achieve the largest color gamut. Traditional CCFL backlighting offers a gamut pretty much covering the sRGB colour space. However, the sRGB space is a little small to use as a reference for colour gamuts and so the larger NTSC colour space tends to be more commonly used nowadays. The sRGB space corresponds to 72% of the NTSC colour space, which is a figure commonly used in modern specifications for standard CCFL backlit monitors. If you read the reviews here, you will see that analysis with colorimeters allows us to measure the colour gamut, and you can easily spot those screens utilising regular CCFL backlighting by the fact their gamut triangle is pretty much mapped to the reference sRGB triangle. The rRGB colour space is lacking most in green hues as compared with the gamut of the human eye.

Above Left: a typical measurement of a standard CCFL backlit monitor, covering pretty much the sRGB colour space, 72% of NTSC colour space
Above Right: a typical measurement of a monitor with enhanced CCFL backlighting, covering more than the sRGB colour space and about 92% of the NTSC space

More recent displays have started to utilise a newer generation of CCF lamps, offering a widened gamut and typically a coverage of the NTSC colour space of 92 - 97%. There is a difference in practice, however. I wouldn’t say a great difference, yet the enhanced-gamut models are certainly better. They produce very pure and deep red and green colors typically which you can notice in normal use. Try to ignore press pictures trying to demonstrate the differences between standard and enhanced CCFL backlighting. These tend to only show pictrues where colour saturation has been increased for the picture of the W-CCFL model, when in fact that isn't actually what is happening. Only the saturation of those colors that don’t fit within the old monitors’ gamut is improved in reality. Another thing to consider is that if you're viewing such press releases on your old monitor, you won’t ever notice the difference because your monitor cannot reproduce such colors anyway! On the other hand, the manufacturers have to show the advantages of the new models one way or another in their press releases.

LED backlighting units come in two flavours typically for desktop monitors, those being White-LED and RGB LED. With White-LED (W-LED) The LED's are placed in a line along the edge of the matrix, and the uniform brightness of the screen is ensured by a special design of the diffuser. The colour gamut is still limited to around 68% NTSC but are cheaper to manufacturer and so are being utilised in more and more screens, even in the more budget range. They do have their environmental benefits as they can be recylced, and they have a thinner profile making them popular in super-slim range models and notebook PC's.

Above: colour gamut of a typical LED backlit display, covering 114% of the NTSC colour space

RGB LED backlighting consists of an LED backlight based on RGB triads, each triad including one red, one green and one blue LED. With RGB LED backlighting the spectrum of each LED is rather wide, so their radiation can’t be called strictly monochromatic and they can’t match a laser display, yet they are much better than the spectrum of CCFL and W-CCFL backlighting. LED backlighting is not common yet in desktop monitors, and their price tends to put them way above the budget of all but professional colour enthusiast and business users. We will probably see more monitors featuring LED backlighting over the coming years, and these models are currently capable of offering a gamut covering > 114% of the NTSC colour space.

Panel manufacturer AU Optronics has successfully developed and commercialized HiColor technology utilizing CCFL backlight to reach a 33% color saturation increase compared with conventional LCDs. Targeting the development trend of LEDs, AUO has further developed the new HiColor Technology with RGB LED backlight. HiColor Technology with LED backlight can reach 105% NTSC, a 45% increase from 72% NTSC. It also provides the true natural performance of Red, Green and Blue and enables bright, rich, and vivid display colors.

In addition, AUO has adopts several specific techniques to enhance the image performance of LED backlights. The Color Management function can eliminate the artificial colors caused by inconsistent chromaticity between the light source and the signal. The Flexible Color Temperature Setting can change the intensity of RGB LEDs to adjust the white point of backlights and meet different application requirements without much luminance loss.

Other advantages of LED backlights include mercury and lead free, instant light, low DC voltage, shock and vibration safe, fast response time, and low temperature start.

You will commonly see a monitor's gamut listed as a percentage compared with a reference colour space. This will vary depending on which reference a manufacturer uses, but commonly you will see a % against the NTSC or Adobe RGB colour spaces. Bear in mind also that the gamut / colour space of the sRGB standard equates to about 72 - 75% of the NTSC reference. This is the standard colour space for the Windows operating system and the internet, and so where extended colour spaces are produced from a monitor, considerations need to be made as to the colour space of the content you are viewing.

Viewing Angles

Viewing angles are quoted in horizontal and vertical fields and often look like this in listed specifications: 170/160 (170° in horizontal viewing field, 160° in vertical). The angles are related to how the image looks as you move away from the central point of view, as it can become darker or lighter, and colours can become distorted as you move away from your central field of view. Because of the pixel orientation, the screen may not be viewable as clearly when looking at the screen from an angle, but viewing angles of TFT’s vary depending on the panel technology used.

As a general rule, the viewing angles are IPS > VA > TN Film. The viewing angles are often over exaggerated in manufacturers specs, especially with TN Film panels where quoted specs of 160 / 160 and now even 170 / 170 are based on overly loose measuring techniques. Be wary of 176/176 figures as these are often over exagerated specs for a TN Film panel and are based on more lapse measurement techniques.

In reality, IPS and VA panels are the only technologies which can truly offer wide viewing fields and are commonly quoted as 178/178. VA panels can sometimes show a colour / contrast distortion as you move slightly away from a central point. While most people do not notice this anomaly, others find it distracting. IPS panels do not suffer from this.

On a CRT monitor, the refresh rate relates to how often the whole screen is refreshed by a cathode ray gun. This is fired down the screen at a certain speed which is determined by the vertical frequency set in your graphics card. If the refresh rate is too low, this can result in flickering of the screen and is often reported to lead to head aches and eye strain. On a CRT, a refresh rate of 72Hz is deemed to be "flicker free", but generally, the higher the refresh rate the better.

TFT screens do not refresh in the same way as a CRT screen does, where the image is redrawn at a certain rate. A TFT monitor will only support refresh rates coming from your graphics card between 60Hz and 75Hz (ignoring modern 120Hz monitors for a moment). Anything outside this will result in a "signal out of range" message or similar. The “recommended” refresh rate for a TFT is 60hz, a value which would be difficult to use on a CRT. The “maximum” refresh rate of a TFT is 75hz, but sometimes if you are using a DVI connection the refresh is capped at 60hz anyway.

As a TFT is a static image, and each pixel refreshes independently, setting the TFT at 60hz does not cause the same problems as it would on a CRT. There is not cathode ray gun redrawing the image as a whole on a TFT. You will not get flicker, which is the main reason for having a high refresh rate on a CRT in the first place. The reason that 60Hz is recommended by all the manufacturers is that it is related to the vertical frequency that TFT panels run at. Some more detailed data sheets for the panels themselves clearly show that the operating vertical frequency is between about 56 and 64Hz, and that the panels 'typically' run at 60Hz (see the LG.Philips LM230W02 datasheet for instance - page 11). If you decide to run your refresh rate from your graphics card above the recommended 60Hz it will work fine, but the interface chip on the monitor will be in charge of scaling the frequency down to 60Hz anyway. The reason that some DVI connections are capped at 60Hz in Windows is that some DVI interface chips cannot scale the frequency properly and so the option to run above 60Hz is disabled. You may find that the screen looks better at 60Hz as you are avoiding the need for the interface chip to scale the resolution. Try it on both and see which you prefer, the monitor can handle either.

One thing which some people are concerned about is the frames per second (fps) which their games can display. This is related to the refresh rate of your screen and graphics card. There is an option for your graphics card to enable a feature called Vsync which synchronizes the frame rate of your graphics card with the operating frequency of your graphics card (i.e. the refresh rate). Without vsync on, the graphics card is not limited in it's frame rate output and so will just output as many frames as it can. This can often result in graphical anomalies including 'tearing' of the image where the screen and graphics card are out of sync and the picture appears mixed as the monitor tries to keep up with the demanding frame rate from the card. To avoid this annoying symptom, vsync needs to be enabled.

With vsync on, the frame rate that your graphics card is determined by the refresh rate you have set in Windows. Capping the refresh rate at 60hz in your display settings limits your graphics card to only output 60fps. If you set the refresh at 75hz then the card is outputting 75fps. What is actually displayed on the monitor might be a different matter though. You can measure the internal frame rate of your system using programs like 'fraps' and also some games report your frame rate. Remember, the frequency of the monitor is still being scaled down to 60Hz by the interface chip. If you are worried about frame rate in fast games then it is a good idea to try the refresh rate at 75Hz and see if you think it looks better. A lot of it could be based on placebo effect though, and if you have a decent graphics card which can handle a constant 60fps it might look just as good as if it were outputting 75fps. See which one you prefer.

One other thing to note for Overdrive (RTC) enabled monitors is that running a TFT outside of it's recommended refresh rate can lead to a deterioration in the performance of this technology and the panel responsiveness is adversely effected! Read the details here.

You will see more mention of higher refresh rates from both LCD televisions and now desktop monitors. It's important to understand the different technologies being used though and what constitutes a 'real' 120Hz and what is 'interpolated':

Pixel Pitch

Unlike on CRT’s where the dot pitch is related to the sharpness of the image, the pixel pitch of a TFT is related to the distance between pixels. This value is fixed and the same for all TFT’s which are the same size. This is because a 17” TFT for instance will always be the same 17” viewable area, and will always have the same number of pixels (1280 x 1024). Pixel pitch is normally listed in the manufacturers specifcation. Generally you need to consider that the 'tighter' the pixel pitch, the smaller the text will be, and potentially the sharper the image will be. To be honest, monitors are produced with a sensible resolution for their size and so even the largest pixel pitches return a sharp images and a reasonable text size. Some people do still prefer the larger-resolution-crammed-into-smaller-screen option though, giving a smaller pixel pitch and smaller text. It's down to choice and ultimately eye-sight.

To calculate the pixel pitch of a given monitor size and resolution, you can use this useful pixel pitch calculator

The aspect ratio of a TFT is related to the ratio of the image in terms of its size. The aspect ratio can be determined by considering the ratio between horizontal and vertical resolutions. While a 20"/21" screen with 1600 x 1200 resolution is a 4:3 ratio, 17" and 19" models are actually 5:4 ratio since their native resolution is 1280 x 1024. Widescreen formats are also available with 16:10 and 16:9 ratios, the latter generally used more for multimedia screens and in the LCD TV market. Widescreen is obviously more useful when it comes to multimedia and movie use. See our widescreen guide for further information as well.

This relates to the connection type from the TFT to your PC. Nearly all TFT’s come with an analogue connection, which is commonly referred to as D-sub or VGA. This allows a connection from the VGA port on your graphics card, where the signal being produced from the graphics card is converted from a pure digital to an analogue signal. There are a number of algorithms implemented in TFT’s which have varying effectiveness in improving the image quality over a VGA connection.

Some TFT’s offer a DVI input as well to allow you to make use of the DVI output from your graphics card which you might have. This will allow a pure digital connection which can sometimes offer an improved image quality. Whether a DVI connection will make any difference to the image quality depends on several things including the model of TFT, quality of VGA connection and graphics card used. Please see this section for < more info >

It is possible to get DVI – VGA converters. These will not offer any improvements over a standard analogue connection, as you are still going through a conversion from digital to analogue somewhere along the line. Some screens also offer other interfaces designed for external devices such as games consoles and DVD players. HDMI, DisplayPort, S-Video, Composite and Component are available on some models if this functionality is appealing and are widely implemented to allow connection of other external devices. Some of these interfaces are also capable of carrying sound as well as video (e.g. HDMI and DisplayPort)

TCO Standards

The TCO standard is related to the specifications of the model as a whole and is a classification system used to certify a TFT.

NTSC (%)	Adobe RGB (%)	ISO Coated (%)
72
92	95	98.5
102	97.8
116	114
125	123

Specifications

LCD and TFT

Screen Size

Refresh Rate

LCD and TFT

Screen Size

Resolution

Panel Type

Response Time

Response Time In More Detail

Response Times and Different Panel Technologies

Response Time Changes and the Introduction of Overdrive

Contrast Ratio

Brightness

Colour Depth

Viewing Angles