LCDs DEMYSTIFIED: How to find the right monitor.
Aug 10, 2006 (Updated Aug 25, 2006) Write an essay on this topic.
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The Bottom Line There is no perfect monitor for all applications, so make sure it fits yours.
LCD monitors are all the hype. Prices are dropping just as fast as new and better models are introduced. CRTs are not completely dead just yet, but the advantages of flat panels are undeniable. How do you pick the right monitor when each brand seems to have the best product ever -- at least according to their side of the story. How do you compare LCDs anyway, and what do need to pay special attention to? Well, you're in the right place to find out ...
TO EACH ITS OWN
Just like we prefer different colors or car brands for that matter, users can be divided in many different groups and all may vary from each other. Overall I see basically three groups of users that may have distinctly different requirements ...
[Professionals] - While there is no specific type of professionals, there are basically two groups of computer users that rely on monitors to interface with their work. Relatively "low" requirements arise from typical office applications like word processing, but size matters and spread sheets (i.e. Excel or Project) and CAD are best on large screens with high resolution. DTP (desktop publishing) professionals and graphics designers are the most demanding regarding color reproduction (a "traditionally" weak area for LCDs and still a domain of CRT monitors). Improvements in backlighting consistency and spectral accuracy, however, have elevated professional grade modern LCDs to match CRTs and eliminate this problem. In fact, EIZO recently introduced LED back lighting which claimed to be as good as or better than professional CRTs.
[Gamers] - Belittled by many "professionals" and computer amateurs alike, gamers are possibly the most demanding computer users second only to professional graphic designers. While larger monitors are great for PC gamers too, it's mostly the response time, viewing angle and black level that matter for games. To minimize ghosting (in videos etc.) a monitor should be capable of less than 16 ms (black-white-black) response. This is equivalent to a 8 ms in the often used grey-grey response. Insufficient Black levels can easily destroy the experience in dark games (or videos) like Doom III. A good indication for a monitor's capabilities would be the contrast ratio. The higher the better and 1000:1 (white to black) is an excellent number though not perfect either. Larger is better, but for gamers that comes at a hefty price. Provided a larger model also boosts resolution, suddenly the 3D graphics card is also taxed a lot more and an upgrade may be inevitable.
[Home Users] - For those that pride themselves of not playing ("childish") games, and otherwise really don't demand much from their computer either, cost is often the most important factor of them all. Sure, big is beautiful but space and budget are often limited. While prices for 15" monitors are very low these days, even 19" are in the $200 range and 17" may really be the best compromise for internet warriors. It's still easy to stow away in even the wimpiest "home office" (or the furniture some chains offer under that category). While on a budget it still doesn't hurt to compare and find the best deal for cost, viewing angle, size and brightness.
IMPORTANT TERMS DEMYSTIFIED
- How important is Brightness?
- What is a Contrast Ratio?
- Do I need to worry about Anti Glare?
- What does the Viewing Angle mean?
- Why does Resolution matter?
- What does Geometry have to do with it?
- What does Refresh Rate mean?
- Why is Response Time so special?
- What are Dead or Hot Pixels?
- What does Color Depth mean?
- What is Color Temperature?
- Do I need Color Calibration?
- What's to know about Ergonomics?
- How to Connect the monitor?
- What to know about Power Consumption
- LCD vs. Plasma Screens
- Are CRTs dead?
- Links
[Brightness] - The emitted light density is typically measured in cd/m2 (candela per square meter) or nits. Both units are interchangeable. A typical value for today's monitors is 250 nits and in most applications that's enough. Bright office spaces may require a little more. The brighter the screen the more attention should be paid to the contrast ratio. (see below) Note that brightness reduces over time as the monitor ages. Further, a bright environment can dim the appearance of any monitor significantly. A hood may improve your picture significantly.
Tip: Don't get blinded by the typically dim setting in a store, make sure you get as close to your target environment as possible when judging a monitor's brightness.
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[Contrast Ratio] - The ratio between the brightest (white) and the darkest (black) image that can be reproduced. LCDs basically filter the white background and the Black typically ends up as a dark Grey. Starting at the white level, the contrast ratio describes best how dark of a black the monitor is able to produce. Older screens with 400:1 ratio work fine with 250 nits or less of brightness but black levels can be overpowered by the backlight. Brighter screens should sport a higher contrast ratio and a good number for today's monitors is between 800:1 and 1000:1. It is important to notice that the contrast ratio is given for perpendicular viewing and angular deviations typically result in contrast reduction. Plasma screens work different and light is produced in each individual cell forming a pixel. For that reason contrast ratio is typically much higher (and Black levels better).
Tip: Predominantly bright pictures require much less contrast ratio than dark ones since small portions of Grey on a mostly white background appear darker than they are.
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[Anti Glare] - Screens are typically made of thin sheets of glass and therefore prone to massive reflection. Especially in bright environments the amount of reflected light competes with the emitted picture and ultimately distracts from the displayed image and even masks darker portions of a picture with the "glare". While there are many ways to reduce the glare more or less effectively, today you will find mostly AR coatings (anti reflective) to be used. Their durability has improved greatly and effectiveness increased too. However, excessive diffusing of the environment light can also reduce the achievable dynamic range (see contrast) due to scattered light and ultimately washed out colors. This is best judged with the monitor turned off at normal lighting. Not only Sony has been notorious for boosting colors by eliminating anti-glare methods ... a potentially annoying path in any bright environment (especially when watching darker content).
Tip: If you can see a reflection of yourself in the monitor, or the screen seems bright Grey when turned off ... there are better options out there. Further, don't get fooled by advertisement implying that you can use a laptop in the bright outdoors. Lack of brightness to compete with the sun and glare typically render the screen unreadable.
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[Viewing Angle] - Hard to measure and sometimes even harder to understand, the viewing angle is a vital parameter in judging the quality of a LCD screen (but not CRTs and seldom Plasma). It describes the ability of seeing the same picture from a wide range of angles. Even when sitting still in front of the monitor, with bigger panels the angle changes drastically between the center and the edges. This may cause annoying inconsistencies. It is important to understand that there is no standardized way of measuring viewing angle, and it sure does not mean to be the point where the picture becomes invisible. Often, you will find a brightness change well below the rated angle, which occasionally recovers slightly past that point. However, brightness reduction is only half the truth. Sometimes you will also notice a significant impact on the Black level (or contrast) with increased viewing angle. This may practically inverse certain color combinations and make for very unsatisfactory results. The spec lists the cone, or twice the actual viewing angle.
Tip: Make sure to view the screen from all four directions to determine changes in brightness and contrast. This is best done with a completely white picture (brightness) and a very dark picture (contrast).
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[Resolution] - The human eye allows to resolve about 5 million pixels with normal eye sight. This is not a practical measure since we tend to focus on a fraction of that. However, resolution is widely mixed up and nowadays the total number of pixels (i.e. 1920x1200) is given in place of the traditional 72 dpi (dots per inch). The latter stems from printing applications and is a measure for how close we can get before seeing individual pixels. While important for printing, monitors gain little value from superfine resolution (>150 dpi). After all, in many cases we have to decipher the displayed information. In today's specs this is typically expressed by the pixel pitch. To match the Windows standard setting of 96 dpi, pixels need to be placed in increments of about 0.264 mm. Resolution on the other hand, now almost exclusively describes the real-estate of your monitor -- measured in pixels. For instance, 1920x1200 pixels can show a total of 2,304,000 pixels which is significantly more information than the 1,341,440 pixels provided by a 1280x1048 resolution.
Tip: Unlike CRTs, LCDs and Plasmas should be operated at their "native resolution" since pixels are exactly defined and deviations require interpolation to display the picture and ultimately cause artifacts or blur.
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[Geometry] - By design, LCD screens don't have any of the CRT's problems like barrel deformation, resulting from the geometric challenges painting a rectangular picture in a distance from a single point (for which the natural canvas would be a "ball"). LCDs don't require complicated correction electronics and adjustments. However, LCDs are not completely trouble free and it's even more important to watch out for brightness inconsistencies (that are not related to viewing angle). Material variation of the substrate and the process can cause such variation and cannot be "adjusted". Advances in pretty much all brands' processes made their occurrence relatively rare and less pronounced.
Tip: When settling for an older model, make sure to pay attention of the uniform brightness distribution. Brighter spots in random location indicate manufacturing problems. This is best seen with a black "picture" like a blank screensaver, provided the backlight is still on.
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[Refresh Rate] - CRTs have a single dot running across the screen line by line in order to paint the picture. That results in each point to be excited only for a short time before the beam moves on to the next "pixel". This requires good high frequency electronics and cheap systems (i.e. TV sets) beat the cost by cheating with the so-called "interlaced" mode where the even lines are in one half picture and the uneven lines in an other. Consequentially your refresh rate is cut in half for the sake of "higher" resolution. To beat this problem, monitors are typically driven on progressive mode (all lines in one picture). However, keeping with the good old 60 Hz (or 50Hz in Europe) is a tough strain on your eyes due to flicker. The official number to beat this problem is 72 Hz (progressive). However, if you never worked with a monitor or are used to 85 Hz or more, even 75 Hz can be quite noticeable. The higher the refresh rate (and resolution) the better the VGA cable needs to be to prevent blurred vision.
Tip: Old habits give bad advice. If you trained yourself to live with 60 Hz flicker you may be unable to see the difference to 85 Hz at first. In fact, many users shy away from the higher frequency since the screen's brightness appears to be reduced. However, once you used the higher frequency for a while you will notice the strain that 60 Hz flicker invokes on your eyes. This applies to CRTs only!
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[Response Time] - A close cousin to the refresh rate in CRTs yet very different. Since LCDs don't draw a picture one dot at a time, the refresh rate is of less significance. While 25 Hz is considered to be the threshold of human perception, the traditional movie rate is 60 Hz (in the US) or 50 Hz (in Europe) mostly due to constraints of the "interlaced" mode. With 60 Hz being the reference, a monitor needs to be able to change a pixel within 16 ms (0.016 sec) to the new value. At the extremes, that means from white to black or reversed. All this means is that content changes at that rate or slower will be complete and without the remains of the previous scene affecting the current one. Those cross influences would be known as ghosting. Movies seldom have such extreme brightness changes and ghosting is hard to recognize even at technically insufficient monitors. Nevertheless, there are now plenty models capable of 16 ms, and no need to settle for a 40 ms model (as they were typical only a few years ago).
Tip: For marketing reasons, companies often specify the more more impressive Grey-Grey value. However, be advised that this is only half the time of a complete change. To avoid ghosting even in extreme scenes, consider the black-white-black value instead.
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[Hot/Dead Pixels] - The bigger the screen and the finer the pitch (density) of the pixels, the greater the chance for any of them to not work properly. Spec typically allow for a few sub-pixels, but in general not more than 10 or 20 (depending on the model). A sub-pixel is any of the three components (Red, Green, Blue) that white light is made of (in a monitor). Together, three sub-pixels form a single pixel. Hot pixels (a.k.a. "bright pixels") typically are the result of a shortcut that causes the cell to be active all the time without any ability to turn it off, hence the backlight is transmitted all the time (bright) in the color of the defective sub-pixel. A dead pixel on the other hand shares the same control issues but stays dark all the time, preventing light from being transmitted. In this case the remaining two still form a composite light. To the viewer it's less noticeable if a single sub-pixel is dark or dead since it typically results in a discoloration unless you're trying to display solid Red, Green or Blue. Processes have greatly improved and the occurrence of either dead or hot pixels visibly reduced. However, to keep process efficiency profitable, manufacturers are still working off specs that allow a few non-functional pixels and reduce the scrap rate.
Tip: To find dead pixels open a window with a solid white background and look for any dots that are not completely white. For hot pixels open a solid black background and look for color spots (Red, Green or Blue).
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[Color Depth] - The vast majority of digital LCD screens is limited to a color depth of 24 bit or 16.7 million colors. It's more correct to speak of shades of color, but the limitation remains. (CRTs allow often 32 bit due to their analog nature.) The digital bandwitdth and processing inside the LCD are responsible for the 24 bit limitation. There are only very few models that at least internally process 32 bit color and I only know of one model from EIZO that actually attempts to even display more than 16 mio shades. The significance for DTP professionals is in subtile transitions, where 24bit sometimes forces banding and doesn't appear smooth. The "culprit" is the DVI-D spec which defines the color depth at 24 bit per pixel. To bypass that you would have to use the analog DVI-A while sacrificing some sharpness. (Lower resolution theoretically would have the bandwidth for 32 bit color information.)
Tip: 24 bit color depth is sufficient for most users. For those interested in easily reproducing the effect, reduce the color depth of your desktop to 256 colors and watch what happens to photos. The difference to 32 bit is much less pronounced and more or less left to a small group of professionals only.
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[Color Temperature] - Don't touch your monitor, this has nothing to do with how hot this device gets (hopefully not "red hot"). It's based on the color tint caused by different light sources. For instances, if you're in a room with fluorescent lighting the overall tint is slightly Green, but the brain compensates for that based on our experience (what white paper looks like etc.). A room lit by predominantly incandescent light shifts the light towards yellow. Passive objects like prints and so on shift along and the brain's compensation is fine. However, monitors are active light sources which are only mildly affected by the sourrounding and a mismatch throws your matching off. A daylight compensated display looks warmer in a fluorescent lighting and so on. Perfect compensation is a tough one and it's preferred to use dim lighting or properly balanced light sources (i.e. daylight light bulbs etc.). Color temperature is easier to understand when using its equivalent in digital cameras: white balance.
Tip: The color temperature setting makes the most sense for brightly lit environment only, where the surrounding "competes" with the picture. In a dim setting, keep it at daylight setting. The same is true for a wild mix of lightsources, but don't expect true colors.
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[Color Calibration] - Most monitors are fairly accurate in their color reproduction for normal application. Calibration is only when it has to be right. The goal is correct the reproduced color to match what the computer thinks it should be. Based on gamma curve and color temperature, the sensor measures the difference and the resulting profile records correction data to tweak the true output of your monitor to get closer to the correct value. The photosensoric hardware is often a little more expensive than most users are willing to invest. Some vendors include simple programs to guess a color profile based on generic correction algorithms. Some vendors even provide color averaged profiles for specific models as downloads.
Tip: Calibration builds on top of your defined color temperature. Make sure to use the correct profile according to your environment before running a tool like the Colorvision Spyder. (Preferably with environment lighting set to minimum.)
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[Ergonomics] - The TCO-99 sticker alone on your screen doesn't make for an ergonomic use. A proper desk and chair for ergonomic posture are just as important. Make sure to have the screen center positioned slightly below eye level. When looking at the screen center, your view should be nearly perpendicular. Eliminate strong light sources such as windows behind you to reduce glare. Further, the screen needs to be shielded from strong ambient light (like some offices) to retain usable contrast. Taking break from the relatively static position in front of the screen is good practice to reduce neck and back strain. While these thingshave little to do with the monitor itself, they sure help to make it more enjoyable. Pick a bezel color based on your environment to reduce strong contrast. Silver blends in better, while Black works well against dark walls (i.e. certain furniture).
Tip: Bezel size is more important for looks than ergonomics, unless you're stuck with high contrast environment like bright background and black bezel. In that case it's best to minimize the contrast by reducing the frame size.
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[Connectivity] - For analog monitors like CRTs there are basically only two ways to connect your monitor to the computer: Sub-DIN (VGA) or Composite. The latter is found in professional grade monitors only and even more rare in graphics boards. Composite allows to separate the RGB signal better and reduced cross talk improves clarity. The higher resolution and refresh rate the greater the difference to VGA. Fundamentally digital monitors like LCD and Plasma are typically able to work with the analog signal. However, be aware that the signal is now converted in the computer from digital to analog and in the monitor back to digital. The double conversion is prone to inaccuracies. To avoid that, a DVI-D (Digital Visual Interface) transmits the digital signal directly to the monitor. There are basically two flavors of DVI-D: Single and Dual Link. In single link mode up to 3.7 Gbit/s can be transmitted, allowing for up to 1920x1200 pixels in 60Hz (165 MHz). In dual link mode it can transmit up to 7.4 Gbit/s since instead of one pixel per clock cycle it now transmits two, allowing for ultra high resolution. However, the color depth is generally defined at 24 bits per pixel. The DVI-A standard is analog and more closely to the composite signal, while the DVI-I is a mix of analog and digital.
Tip: Dual link cables are expensive and only used for extreme resolution monitors (> 1920x1200px). DVI (digital) connectors are white and VGA (analog) connectors typically blue.
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[Power Consumption] - Granted, this potentially is a rather complex issue once you include production and disposal issues in the mix, but a relatively easy measure is the power consumption of your monitor as such. There are typically at least two stages of which the sleep mode consumes roughly 5W or less (driven by EnergyStar requirements). In use the power consumption naturally varies greatly depending on size and brightness. LCD monitor typically range between 40W and 100W, about 30% - 50% less than comparable CRT monitors. The main source in LCDs is the backlighting. Reducing it to your needs can also minimize the true power consumption. Sleep mode is not to be underestimated either, 5W may not seem like a lot, but consider millions of households and it makes a difference. Most computers spend the majority of the day unused. Turning off the monitor via power button is still fabled to reduce it's life, but today it's not much more than a persistent left-over from old times. I have been using many monitors in my 20 computer years. I actually have never seen one go bad because I turn it off every time when not in use for more than half an hour. (In the office I am virtually the only one who does, and believe it or not mine lasts longer!)
Tip: So-called screensavers are as up-to-date as CRTs. They don't do anything for LCDs other than displaying "pretty" pictures and keeping power consumption up. Select an EnergyStar compatible powersave mode instead to turn off the back light.
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[LCD vs. Plasma] - There are practically no Plasma computer monitors due to achievable resolution in that technology. However, the selection is relatively easy should you consider one. This rule of thumb works for most models, but exceptions may apply. LCDs provide more brightness and potentially more resolution while Plasmas simply provide better viewing angles and black levels (contrast ratio). So in a nutshell, Plasma is superior for watching movies in normal lit environments. LCDs, on the other hand, are better monitors and easier to work with. Never mind that LCDs are also a lot cheaper. Plasmas got a bad name due to the dreaded "burn-in" effect (which also CRTs had a tough time with), but not only has the technology improved in this regard, but it's also blown out of proportion. The burn-in is mostly known from extreme examples like airport flight schedule displays that show the same information for minutes at a time. The static picture in return caused "premature" fatigue (showing a memory effect).
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[Are CRTs dead?] - Almost, but not quite! Some existing CRTs may not be replaced for another 5 - 10 years. Professional applications that require absolute truth in color control may even get new models for a while as they're still unbeatable in price. However, as CRTs become rare the mass-production advantages go away and LCDs will eventually eliminate CRTs on a large scale. However, if you're happy with your tube, you might as well prolong its life and wait for even better LCD monitors at lower cost ... not too far away. Oh and in case you're wondering what CRT stands for: Cathode Ray Tube (the stuff traditional TVs are made of).
© 2006, theuerkorn
LINKS
Monitors:
- Samsung SyncMaster 244T ***** (2006)
- ViewSonic VP201s ****- (2005)
- Samsung SyncMaster 940B ***-- (2006)
- Planar PX171M ***-- (2003)
Calibration:
- Colorvision Spyder
Graphics Cards:
- ATI Radeon x1900 XT ***** (2006)
- ATI Radeon x1800 XL ****- (2005)
- MSI Radeon x800 XL ***-- (2005)
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