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SpecificationsLCD and TFT Classification

Screen Size

Aspect Ratio

ResolutionPanel Type

TN Film (Twisted Nematic + Film)

IPS (In Plane Switching)

MVA (Multi-Domain Vertical Alignment)

PVA (Patterned Vertical Alignment)

PLS (Plane to Line Switching)

Detailed Panel Technologies Article

Advanced Super View (ASV)

Advanced Fringe Field Switching (AFFS)

Super Fine TFT Technology (SFT)

Response Time

Summary

Detailed

Different Panel Technologies

Overdrive

How Response Time Is Reviewed

Contrast Ratio

Brightness

Colour Depth

Colour Space / Gamut and Backlighting Type

CCFL Backlighting

Wide Colour Gamut CCFL Backlighting (WCG-CCFL)LED Backlighting

Gamut References

Viewing Angles

Refresh Rate

Pixel Pitch

Power Consumption

Interfaces and Connectivity

TCO Standards

LCD and TFT Classification

Central http://www.tftcentral.co.uk/specco

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LCD stands for "Liquid Crystal Display" and TFT stands for "Thin Fi lm Transistor". These two terms are

used commonly in the industry but refer to the same technology and are really interchangeable when

talking about certain technology screens. The TFT terminology is often used more when describing

desktop displays, whereas LCD is more commonly used when describing TV sets. Don't be confused by

the different names as ultimately they are one and the same. You may also see reference to "LED

displays" but the term is used incorrectly in many cases. The LED name refers only to the backlight

technology used, which ultimately still sits behind an liquid crystal panel (LCD/TFT).

Screen Size

As TFT screens are measured differently to older CRT monitors, the quoted screen size is actually the

full viewable size of the screen. This is measured diagonally from corner to corner. TFT displays are

available in a wide range of sizes and aspect ratios now. More information about the common sizes of

TFT screens available can be seen in our section about resolution.

Aspect Ratio

The aspect ratio of a TFT describes 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 5:4 ratio since their native

resolution is 1280 x 1024. Widescreen formats are increasingly common, with 16:10 and 16:9 ratios,

the latter generally used more for multimedia screens and in the LCD TV market.


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Resolution

The resolution of a TFT is an important thing to consider. All TFTs 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. 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. Also keep in

mind whether you are planning to connect external devices and the resolution they are designed to

run at.

As a guide to the common resolutions available:

ScreenSize

(diagonalinches)

CommonResolution

Other ResolutionsCommonly 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 9001366 x 768, 1680x

1050

20 1600 x 1200 1400 x 1050

20 WS 1680 x 1050 1600 x 900

21 1600 x 1200 2048 x 1536

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

23.1 WS 1600 x 1200

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 2560 x 14401920 x 1080, 2048 x1152, 1920 x 1200

28 WS 1920 x 1200 -

30 WS 2560 x 1600 -


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High Definition Resolution Support

More and more you will see resolutions referred to by their common HD equivalents. HD content is

based purely on the resolution of the source and is commonly defined by the number of pixels

vertically 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 video 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 at least a vertical resolution of 1080 pixels, e.g. a1920 x 1080 monitor.

Panel Type

While this aspect is not always discussed by display manufacturers it is a very important area to

consider when selecting a TFT monitor. The LCD panels producing the image are manufactured by

many different panel vendors and most importantly, the technology of those panels varies. Different

panel technologies will offer different performance characteristics which you need to be aware of.

Their implementation is dependent on the panel size mostly as they vary in production costs and in

target markets. The four main types of panel technology used in the desktop monitor market are:

TN film (Twisted Nematic + Film)

TN Film was the first panel technology to be widely used in the desktop monitor market and is still

regularly implemented in screens of all sizes thanks to its comparatively low production costs. TN

Film is generally characterized by good pixel responsiveness making it a popular choice for gamer-

orientated screens. Where overdrive technologies are also applied the responsiveness is improved

further. TN Film panels are also available supporting 120Hz refresh rates making them a popular

choice for stereoscopic 3D compatible screens. While older TN Film panels were criticized for their

poor black depth and contrast ratios, modern panels are actually very good in this regard, often

producing a static contrast ratio of up to 1000:1. Perhaps the main limitation with TN Film technology

is its restrictive viewing angles, particularly in the vertical field. While specs on paper might look


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promising, in reality the viewing angles are restrictive and there are noticeable contrast and gamma

shifts as you change your line of sight. TN Film panels are normally based around a 6-bit colour

depth as well, with a Frame Rate Control (FRC) stage added to boost the colour palette. They are

often excluded from higher end screens or by colour enthusiasts due to this lower colour depth and

for their viewing angle limitations. TN Film panels are regularly used in general lower end and office

screens due to cost, and are very popular in gaming screens thanks to their low response times and

120Hz support. Pretty much all of the main panel manufacturers produce TN Film panels and all are

widely used (and often interchanged) by the screen manufacturers.

IPS (In Plane Switching)

IPS was originally introduced to try and improve on some of the drawbacks of TN Film. It was

developed by Hitachi and was dubbed "super TFT". Production costs were high and so IPS technology

was reserved for high end and professional grade screens only. While initially viewing angles were

improved, the panel technology was traditionally fairly poor when it came to response times and

contrast ratios. Production costs were eventually reduced and the main investor in this technology

has been LG.Display (formerly LG.Philips). The original IPS panels were developed into the so-called

Super IPS (S-IPS) generation and started to be more widely used in mainstream displays. These

were characterized by their good colour reproduction qualities, 8-bit colour depth (without the need

for Frame Rate Control) and very wide viewing angles. These panels were traditionally still quite slow

when it came to pixel response times however and contrast ratios were mediocre. In more recent

years a change was made to the pixel alignment in these IPS panels (see our detailed panel

technology article for more information) which gave rise to the so-called Horizontal-IPS (H-IPS)

classification. With the introduction of overdrive technologies, response times were improved

significantly, finally making IPS a viable choice for gaming. This has resulted more recently in IPS

panels being often regarded as the best all-round technology and a popular choice for display

manufacturers in today's market. Improvements in energy consumption and reduced production costs

lead to the generation of so-called e-IPS panels. Unlike normal 8-bit S-IPS and H-IPS classification

panels, the e-IPS generation worked with a 6-bit + FRC colour depth. Developments and

improvements with colour depths also gave rise to a generation of "10-bit" panels with some

manufacturers inventing new names for the panels they were using, including the co-called

Performance-IPS (p-IPS). It is important to understand that these different variants are

ultimately very similar and the names are often interchanged by different display vendors. For moreinformation, see our detailed panel technologies guide.

VA (Vertical Alignment)

The original early VA panels were quickly scrapped due to their poor viewing angles, and in their

place came the two main types of VA matrix. Multi-Domain Vertical Alignment (MVA) and

Patterned Vertical Alignment (PVA) panels. These VA variants were characterized by their

reasonably wide viewing angles, being better than TN Film but not as wide as IPS. They were

originally poor when it came to pixel response times but offered 8-bit colour depths and the best

static contrast ratios of all the technologies discussed here. Traditionally VA panels were capable of

static contrast ratios of around 1000 - 1200:1 but this has even been improved now to 3000:1 andabove. Until very recently VA panels remained very slow and so were not really suitable for gaming.

However during 2012 we have seen advancements with the latest generation of VA panels and

through the use of overdrive technologies this has been significantly improved. Perhaps the main

limitation with VA panels is still their viewing angles when compared with popular IPS panel options.

Gamma and contrast shifts can be an issue and the technology also suffers from an inherent

off-centre contrast shift issue which can be distracting to some users. Through the years we have

seen several different generations of VA panels. AU Optronics are the main manufacturer of MVA

matrices, and we have seen the so-called Premium-MVA (P-MVA) and Advanced-MVA (AMVA)

generations emerge. Chi Mei Innolux (previously Chi Mei Optoelectronics / CMO) also make their own

variant of MVA which they call Super-MVA (S-MVA). The only manufacturer of PVA panels is


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Samsung as it is their own version of VA technology. We have seen several generations from them

including Super-PVA (S-PVA) and cPVA. For more information, see our detailed panel technologies

guide.

PLS (Plane to Line Switching)

Due to the popularity of IPS technology in the market, Samsung took a step away from their PVA

investment and introduced a new panel technology in 2011. It was designed to offer wide viewing

angles similar to IPS and offer improvements over some of the limitations of Samsung's PVA

technology. While the technology is still in its infancy, it shows promising performance in terms of

colour reproduction, black depth and responsiveness as well. 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. 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 sectors. 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 areas between pixels, horizontally aligned electric fields and replaced

metal electrodes with transparent ones. More information about AFFS can be found here.

Super Fine TFT Technology (SFT)

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 there, 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.


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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. More information is available from NEC LCD

Response Time

Response Time is the spec which many people, especially gamers, have come to regard as the most

important. In practical terms the spec is designed to refer to the speed of the liquid crystal 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 and ghosting in games and

movies which can be an issue if response time is too slow. As a general rule of thumb, 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

monitors 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 togrey 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.


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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. This measurement of the black > white > black transition was defined as the ISO

standard for response time measurements.

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 transit ions are in shades

of grey, and are then passed through the colour filters. The speed of change 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 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 defines the grey

scale ranging 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. It is the fastest 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-overdriven, TN Film panel.

As you can see from the graph, the actual response time can vary quite considerably across the


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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 TFTs 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 (we are assuming for now non-overdriven panels):

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 as well as to

consider real-life responsiveness tests such as those we carry out in our reviews.

Response Time Changes and the Introduction of Overdrive


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Overdrive or 'Response Time Compensation' (RTC) is a technology which is designed to boost the

response times of pixels across all transitions, with particular focus on improving the grey to grey

changes. It is achieved by sending an over-voltage to the pixels to make them change orientation

more quickly. While the full black > white change remains largely unchanged (since it already

received the maximum voltage anyway), improvements across other transitions are often dramatic.

With the introduction of overdriven 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 changeaway 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 to grey transitions

are now significantly improved, and response times of 2 - 5ms G2G are now common place. These

technologies have allow significant improvements in all panel technologies, but particularly in IPS

and VA panels where response times were previously poor.

How Response Time Is Reviewed

Some reviews sites have access to advanced photosensor (photodiod + low-noise operational

amplifier) and oscilloscope measurement 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 in practice and what a user might see in normal use. I think it is important to study both

methods if possible to give a fuller picture of a panels performance. TFT Central uses 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 moving car test as shown here:

Perfect screen with no notable blurring / ghosting

Screen shows ghosting of 3 images


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Movement isnt 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 and where these are too aggressively applied, or poorly controlled, it can result in

problems. In this case, an image can appear in front or behind the main object, creating a white or

dark halo commonly.

We use this software to test the monitors we review, capturing images using a camera and comparing

the best case and worst case examples. This gives us a good way to compare screens side by side and

evaluate a screens responsiveness in practice.

Contrast Ratio

The Contrast Ratio of a TFT is the difference between the darkest black and the brightest white it is

able to display. This is really defined by the pixel structure and how effectively it can let light through

and block light out from the backlight unit. As a rule of thumb, the higher the contrast ratio, thebetter. The depth of blacks and the brightness of the whites are better with a higher contrast ratio.

This is also referred to as the static 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. Figures of 3000:1 and above are now available using modern

AMVA and cPVA panels.

Some technologies boast the ability to dynamically control contrast (Dynamic Contrast Ratio - DCR)

and offer much higher contrast ratios which are incredibly high (millions:1 for instance!). Be wary of

these specs as they are dynamic only, and the technology is not always very useful inpractice. 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. Black point is also tied in to contrast

ratio. The lower the black point, the better, as this will ensure detail is not lost in dark image when

trying to distinguish between different shades.

Brightness / Luminance

Brightness as a specification is a measure of the brightest white the TFT can display, and is moreaccurately referred to as its luminance. Typically TFTs 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. Default brightness of screens out of the box is regularly

much higher so you need to consider whether the monitor controls afford you a decent adjustment

range and the ability to reduce the luminance to a comfortable level based on your ambient lighting

conditions. Different uses may require different brightness settings as well.


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Colour Depth

The colour depth of a TFT panel 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 ColourDepth

Total BitsPer Colour

Steps PerSub pixel

TotalColours

6-bit 18-bit 64 262,1446-bit + FRC - - 16.2 million

8-bit 24-bit 256 16.7 million

8-bit + FRC "30-bit" 256 1.07 billion10-bit 30-bit 1024 1.07 billion

The colour depth of a panel is determined really by the number of possible 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 = 64x 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.

Spatial Dithering - The dithering method involves assigning appropriate colour values from

the available colour palette to close-by pixels in such a way that it gives the impression of a

new colour tone which otherwise could not have been created at all. In doing so, there complex

mappings according to which the ground colours are mutually assigned, otherwise it could

result in colour noise / dithering noise. Dithering can be used to allow 6-Bit panels, like TNFilm, to show 16.2 million perceived colours. This can however sometimes be detectable to the

user, and can result in chessboard like patterns being visible in some cases.

Frame Rate Control / Temporal Dithering - The other method is Frame-Rate-Control (FRC),

also referred to sometimes as temporal dithering. This works by combining four colour frames

as a sequence in time, resulting in perceived mixture. In basic terms, it involves flashing

between two colour tones rapidly to give the impression of a third tone, not normally available

in the palette. This allows a total of 16.2 reproducible million colours. Thanks to Frame-

Rate-Control, TN panel monitors have come pretty close to matching the colours and image

quality of VA or IPS panel technology, but there are a number of FRC algorithms which vary in

their effectiveness. Sometimes, a twinkling artefact can be seen, particularly in darker shades,

which is a side affect of such technologies. Some TN Film panels are now quoted as being 16.7

million colours, and this is down to new processes allowing these panels to offer a better colour

depth compared with older TN panels.

Other panel technologies however can offer more possible pixel orientations 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 8-bit, without FRC). These are referred to as

8-bit panels with 24-bit colour (8-bit per sub pixel = 8 + 8 + 8 = 24). While most IPS and VA panels

support 8-bit colour, modern e-IPS and cPVA panels do sometimes use 6-bit + FRC instead. See this

news piece for further information.


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10-bit colour depth is typically only used for very high end graphics uses and in professional grade

monitors. There are three main ways of implementing 10-bit colour depth support. Most screens

which are advertised as having 10-bit support are actually using true 8-bit panels. There is an

additional FRC stage added to extend the colour palette. This FRC can be applied either on the panel

side (8-bit + FRC panels) or on the monitor LUT/electronics side. Either way, the screen simulates a

larger colour depth and does not offer a 'true' 10-bit support. You can also only make use of this

10-bit support if you have a full end-to-end 10-bit workflow, including a supporting software,

graphics card and operating system. There are a few 'true' 10-bit panels available but these are

prohibitively expensive and rarely used at the moment. See our panel parts database for more

information about different panels.

Colour Space / Gamut and Backlighting Type

Colour gamut in TFT monitors refers to the range of colours the screen is capable of displaying, and

how much of a given reference colour space it might be able to display. It is ultimately linked to

backlight technology and not to the panel itself.

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 colours our eyes can perceive. Its graphical

representation is called a CIE diagram as shown in the image above. All the colours perceived by the

eye are within the collared area. The borderline of this area is made up of pure, monochromatic

colours. The interior corresponds to non-monochromic colours, 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

colours 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 colour looks very cold,

bluish.


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Above: CIE diagram showing total gamut range of the human eye

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 colours 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 colour gamut.


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Above: gamut triangle of a laser display

Laser Displays are capable of producing the biggest colour gamut for a system with three basic

colours, but even a laser display cannot reproduce all the colours 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

Ill discuss below), the spectrum of each of the basic colours 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 centre.


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Above:sRGB colour space triangle

The colour space produced by any given TFT monitor is defined by its backlighting unit and is not

influenced by the panel technology.

Traditionally, LCD monitors were capable of giving approximate coverage of the sRGB reference

colour space as shown in the diagram above. This is defined by the backlighting used in these

displays - Cold-cathode fluorescent lamps (CCFL) that are employed which emit radiation in the

ultraviolet range which is transformed into white colour with the phosphors on the lamps 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 lamps light. This portion must be as narrow as possible to achieve the largest colour

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 in specifications for colour gamuts and so the

larger NTSC colour space reference tends to be more commonly referred to nowadays. The sRGB

space corresponds to approximately 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 colorimeter devices 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 sRGB colour space is lacking most in green hues as

compared with the gamut of the human eye. It should be noted that most content is produced based

on the sRGB colour space, including Windows, many popular applications and internet content.

Wide Colour Gamut CCFL Backlighting (WCG-CCFL)


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Above Left: a typical measurement of a standard CCFL backlit monitor, covering pretty much the sRGB colour space, 72%

of NTSC colour spaceAbove 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

To help develop and improve on the colour space a screen is capable of displaying some have started

to utilise a newer generation of CCFL backlighting. These so-called "wide gamut" backlights allow a

gamut coverage of typically 92 - 102% of the NTSC colour space. There is a difference in practice as

well which all users should be able to detect. The colour space available is extended mainly in green

shades as you can see from the image above. Red coverage is also extended in some cases. This

extended colour space sounds appealing on face value since the screens featuring WCG-CCFL

backlighting can offer a broader range of colours. Manufacturers will often promote the colour space

coverage of their screens with these high figures. In practice you need to consider what impact this

would have on your use.

It's important to consider what colour space your content is based around. sRGB has long been the

preferred colour space of all monitors, and is in fact the reference for the Windows operating systemand the internet. As such, most content an average user would ever use is based on sRGB. If you

view sRGB content on a wide gamut screen then this can lead to some colours looking incorrect as

they are not mapped correctly to the output device. In practice this can lead to oversaturation, and

greens and reds can often appear false, oversaturated or neon-like. Colour managed applications and

a colour managed workflow can prevent this but for the average user the cross-compatibility of

widely used sRGB content and a wide gamut screen may present problems and prove troublesome.

Some users don't object to the over saturated and 'cartoony' colours for their use, but to many, it is

an issue.

Of course the opposite is true if in fact you are working with content which is based on a wider colour

space. In photography, the Adobe RGB colour space is often used and is wider than the sRGB


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reference. If you are working with wide gamut content, with wide gamut supported applications, you

would want a screen that can correctly display the full range of colours. This could not be achieved

using a traditional CCFL backlit display with only sRGB coverage, and so a wide gamut screen would

be needed. Wide gamut displays are often aimed at colour enthusiasts and professional uses as a

result.

A compromise is sometimes available in the form of a screen which can support a range of colour

spaces accurately. Some higher end screens come with a wide gamut backlight unit. Natively these

offer a gamut covering 92 - 102% of the NTSC colour space. However, they also feature emulation

modes which can simulate a smaller colour space. These emulation modes are normally available

through the OSD menu and offer varying options with varying degrees of reliability. In the best cases

the screens can emulate the smaller Adobe RGB colour space, and also the sRGB colour space. This

allows the user to work in whichever colour space they prefer but gives them compatibility with a

wider range of content if they have the need. The success of these colour space emulations will vary

from one screen to another however and are not always accurate.

Further reading: X-bit Labs Article

LED Backlighting

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 limited to around 68 - 72% NTSC but the units 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 recycled, and they have a thinner profile making them popular

in super-slim range models and notebook PC's. These W-LED backlit screens are considered standard

gamut offerings, equivalent to traditional (normal) CCFL units.


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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 cant be called strictly monochromatic and they cant match a laser display, yet they

are much better than the spectrum of CCFL and WCG-CCFL backlighting. RGB LED backlighting is notcommon 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 RGB

LED backlighting over the coming years, and these models are currently capable of offering a gamut

covering > 114% of the NTSC colour space.

Further reading: LED Backlighting Article

Gamut References


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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.

Here is how several of the colour spaces are linked:

NTSC (%)Adobe RGB

(%)

72

92 95

102 97.8

116 114

125 123

Further information:

X-bit Labs Gamut Information

X-bit Labs - Extended Colour Gamuts Highs and Lows

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 TFTs vary depending on the panel technology used.


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As a general rule, the viewing angles are IPS / PLS > 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 even 170 / 170 are based on overly loose measuring techniques. Be wary of 176/176

figures as these are often over exaggerated specs for a TN Film panel and are based on more lapse

measurement techniques as well.

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 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. They also show more apparent contrast and gamma shifts with changes in the users line

of sight. IPS panels do not suffer from this and are generally considered the superior technology for

wide fields of view. PLS panels while very new are also able to offer wide viewing angles which arecomparable to IPS.

Further reading: ViewSonic's Whitepaper - Why Viewing Angle is a Key Element in Choosing an LCD

Refresh Rate


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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 thescreen 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 and it will not

allow you to select a higher refresh rate from your graphics card.

As a TFT is a static image, and each pixel refreshes independently, setting the TFT at 60hz does notcause the same problems as it would on a CRT. There is no 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


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interface chip to scale the resolution. Try it on both and see which you prefer, the monitor can handle

either in many cases.

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. In some cases forcing a higher refresh rate (even above

75Hz) is possible, but this can have mixed results. In many cases frames are dropped anyway and so

it makes no difference to the end result.

One other thing to note for Overdrive (RTC) enabled monitors is that running a TFT outside of it's

recommended refresh rate can sometimes lead to a deterioration in the performance of this

technology and the panel responsiveness is adversely effected! Read the details here.

120Hz Monitors and LCD TV's

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':

Interpolated 120Hz+ - These technologies are the ones commonly used in LCD TV's where TV

signal input is limited to 50 / 60 Hz anyway (depending on PAL vs NTSC). To help overcome the

issues relating to motion blur on such sets, manufacturers began to introduce a technology to

artificially boost the frame rate of the screen. This is done by an internal processing within the

hardware which adds an intermediate and interpolated (guessed / calculated) frame between

each real frame, boosting from 50 / 60fps to 100 / 120 fps. This technology can offer a

noticeable improvement in practice when it is controlled very well. Some sets even have 240and 480Hz technologies which operate in the same way, but with further interpolation and

inserted frames. See here for further information.

True 120HZ technology - to have a true 120Hz screen, it must be capable of accepting a full

120Hz signal output from a device (e.g. a graphics card). Because TV's are limited at the

moment by their input sources they tend to use the above interpolation technology, but with

the advent of 3D TV and higher frequency input sources, this will change. Desktop monitors are

a different matter though as graphics cards can obviously output a true 120Hz if you have a

decent enough card. Some models can accept a 120Hz signal but need different interfaces to

cope (e.g. dual-link DVI or DisplayPort). These monitors are also introduced with the

development of3D gaming so will no doubt become more and more mainstream. Again these


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offer obvious advantages in terms of gaming where a frame rate of >60fps can be properly

displayed. It also helps improve any motion blur and produce smoother movement in practice,

even helping to remove some overdrive artefacts in some cases. Please see here for further

information

Pixel Pitch

Unlike on CRTs 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 TFTs which are the

same size. This is because a 19 TFT for instance will always be the same 19 viewable area, and will

always have the same number of pixels (1280 x 1024). Pixel pitch is normally listed i n the

manufacturers specification. 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

normally 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 pitchcalculator

Power Consumption

Manufacturer specifications will usually list power consumption levels for the monitor which tell you

the typical power usage you can expect from their model. This can help give you an idea of running

costs, carbon footprint and electricity demands which are particularly important when you're talking

about multiple monitors or a large office environment. Power consumption of an LCD monitor is


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typically impacted by 3 areas:

1) Brightness and the intensity of the backlight - turning up the brightness control on a

screen will normally result in a higher power usage

2) Backlight type - LED backlight units can typically offer lower power consumption than

CCFL units (when running at the same luminance level)

3) Connected peripherals - additional connections like USB powered devices can add

additional pull on the power consumption

Specs will often list a typical usage for the screen, normally related to whatever the default factory

brightness control / luminance is. They may also list a maximum usage, when brightness is turned up

to full and sometimes also an additional maximum when USB ports are in use. A standby power

usage is often also included indicating the power draw when the screen is in standby mode. Some

screens also feature various presets or modes designed to help limit power consumption, often just

involving preset brightness settings. Again these can be useful in multi-monitor environments.

Some technologies are also available to help reduce power consumption. These include ambient light

sensors and human sensors.

Interfaces and Connectivity

This relates to the connection type from the TFT to your PC or other external device. Nearly all TFTs

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 TFTs which have varying effectiveness in improving the image quality

over a VGA connection.

Some TFTs 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 >


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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). With many modern graphics cards also offering HDMI and DisplayPort

connections, the availability of these on a monitor is very useful.

It should also be noted that each interface type can handle different resolutions and bandwidths and

so there are limitations to using certain connections with certain resolutions or refresh rates. As an

example, a 120Hz compatible screen running at 1920 x 1080 resolution needs a special DVI

connection to handle the bandwidth needed. This is referred to as Dual-link DVI which despite it's

name, is just a single DVI connection on your graphics card / screen with more pins on it. A special

DL-DVI cable is also required. DisplayPort is also capable of supporting high bandwidths and so is an

alternative used by some graphics cards for 120Hz support.

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.

TCO- labelling of media displays guarantees:

Ergonomics

-High visual ergonomic requirement on the picture screen which brings with it high picture

quality and good color rendition. Good quality even when the screen displays moving pictures

by means of short response time, good black level and expanded requirement of grey levels.

Emission

-Substantial reduction of magnetic and electrical fields.

Energy

-Low energy consumption in stand-by mode

Ecology


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-That the manufactures are certified according to ISO 14001 or EMAS

-Reduced dispersion into the environment of brominating and chloridizing flame-resistant

material and heavy metals (complying even with RoHS directive from 1st of July 2006).

-That the display unit is pre-prepared for recycling which facilitates recycling of materials.

Please see http://www.tcodevelopment.com/ for more info on which standard a TFT

meets.


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