The Eyes Have It

Choosing an appropriate display can often get very confusing, particularly if you don't know the terminology. We've covered this in our display reviews, so if you're not sure what the various specifications mean you can start there. One area that we didn't cover in that glossary is panel technologies, but once again we've discussed that elsewhere. For those that don't like to follow links, here's a recap.

Many LCD specifications are prone to inflation by the manufacturers or have become largely meaningless. Take contrast ratio for example. That's the white level divided by the black level, and if you could actually get pure black on any LCD contrast ratio would be "infinity". In practice, anything over 500:1 is sufficient, and 1000:1 is about the best you can see before the manufacturers start playing tricks. What sort of tricks? How about dynamic contrast ratio, where the backlight intensity changes according to the content currently being shown on the display. Now you can take the maximum white level at maximum brightness and divide it by the minimum black level at minimum brightness, which results in substantially higher contrast ratios. Unfortunately, in practice the varying intensity of the backlight can be distracting to say the least, and color accuracy greatly suffers because of the constantly shifting brightness levels. Our advice: ignore dynamic contrast ratios, and if your display supports the feature we recommend disabling it.

Pixel response times are another area that has been inflated -- or deflated in this case. We have looked at various LCDs boasting anywhere from a 2ms to 16ms response time; honestly, we would be hard-pressed to tell the difference between most of them. All of the comparison images we've captured show similar best/worst case scenarios for pixel response latency, with one or two afterimages present. A bigger problem these days is processing lag (aka "input lag"), which is the delay between the time a signal is sent to your LCD and the time the internal circuitry finishes processing it and actually shows it on the LCD panel. We have measured lag as high as 50ms, which makes gaming very frustrating and is even noticeable/irritating during general Windows usage.

The one item that manufacturers don't usually make a big deal about happens to be the aspect of any display that seems to matter most: the actual panel technology. There are three general categories of panel technology: TN (twisted nematic), MVA/PVA (multi-domain vertical alignment/patterned vertical alignment), and IPS (in-plane switching). Opinions about which technology is actually best differ somewhat, but there's no denying the fact that TN is substantially cheaper to produce whereas PVA and IPS are more expensive. These days, the vast majority of LCDs are once again using TN panels, largely because of the pricing advantage. If you want a higher quality panel using MVA, PVA, or IPS you will need to be prepared to pay anywhere from 50% to 300% more -- depending on overall quality and the target market. Here's a quick overview of the panel technologies.

Viewing angles on TN are substantially worse, particularly vertical viewing angles, and all TN panels are natively 6-bit panels that use dithering to approximate 8-bit color. Most people won't notice the difference in color accuracy, but imaging professionals would definitely prefer something better. The advantage of TN panels is that -- at least on the ones we've tested -- input lag is not a problem. Response times are usually lower on paper, but again it's difficult to actually see the difference between a 2ms panel and a 6ms panel, especially when the display refreshes every 17ms.

PVA and IPS are basically the exact opposite of TN: great viewing angles, very good color reproduction, and true 8-bit colors. However, pixel response times are a little lower (it's not something that has ever bothered us). The other big problem? At least on the S-PVA panels that we've tested, input lag has been a major concern, ranging from as low as 20ms up to nearly 50ms. Ouch! S-IPS panels don't seem to have a problem with input lag, at least on the models we've tested -- which all happen to be 30" LCDs. That said, Dell's 3008WFP is the exception, which seems to be caused more by the digital scaler than by the IPS panel.

A less common panel type is MVA, which in practice is similar to PVA but seems to perform better in regards to input lag. We've only tested one LCD that uses an MVA panel, the BenQ FP241VW (a review is forthcoming), and input lag appears to be equal to that of our reference LCD. Color quality and other aspects are also good, but pricing and availability is a concern, not to mention the fact that we're not super keen on the frame/stand for the FP241VW.

That was a really long-winded introduction to our display choices, but it's important to understand the above information before you start looking at the various options. Frequently, the choice will come down to getting something larger with a cheaper TN panel versus getting a smaller LCD with a PVA/IPS panel. Even among the same panel technology, however, there are wide variations in quality. Most LCD panels are manufactured by one of only a few companies, but similar to processors these panels are "binned" based on quality. The bottom line is that you often get what you pay for, so if you're wondering why LCD X seems to have the same specifications as LCD Y but costs significantly less, it's very likely that the panel doesn't meet the same quality standards. Color uniformity is one of the big differences between various LCD panels, with the best panels often ending up in displays that cost twice as much as LCDs that are otherwise equal in terms of specs. So now let's look at our various recommendations for the different price points.

LCD Recommendations


View All Comments

  • anandtech02148 - Thursday, December 18, 2008 - link

    nice review,
    I bought the Dell 2408 when it was 512, price have drop a little in 4weeks. Regarding input lag, some suggest using hdmi cable to connect instead of dvi to improve signal lag. Does this really work?

  • Spivonious - Thursday, December 18, 2008 - link

    I wouldn't see why. HDMI is DVI+Audio. Reply
  • USRFobiwan - Thursday, December 18, 2008 - link

    Nice but a little short I think. I have one thing I do not agree on HD TV's and their lag story. What about all the people that play their Xboxes and PS3's. Never seen any lag on those on the big screen

  • dijuremo - Thursday, December 18, 2008 - link

    He taking about input lag, not response time. Take a look at this:">

    It has an animation/video where you can clearly see the LCD is running behing the CRT. Now you should realize how those kids frag you so much in counterstrike using their old CRT... :)
  • HollyDOL - Thursday, December 18, 2008 - link

    well, human optical nerves have reuse downtime of about 35-40ms, so anything below that is unrecognisable for human... Count in brain cheating with the image big way as well and you find out there is no chance to detect that without some device help. Reply
  • Spivonious - Thursday, December 18, 2008 - link

    Ever noticed flicker in a 60Hz or even a 75Hz monitor? I have. That means my eye can pick up changes of 13ms. Reply
  • HollyDOL - Thursday, December 18, 2008 - link

    You are mixing two things together. First of all, CRT monitor flickering you can see is result of your eye catching with various pixel intesities over time... While LCD screen pixel loses only relatively small part of intensity before it gets refreshed, CRT screen pixel virtualy goes between nothing and everything every time. I'll try to find out pictures describing it and post it here later.

    Hard fact is that data running from your eyes to brain is transfered as a electrical currency (=fast) only inside neurons. Two neurons transfer the 'bit' between themselves using chemical reaction of Natrium - Kalium bridge. Simple as that to be able to transfer next bit, the chemical levels need to rebalance and perform further chemical processes to provide that and thus you have got huge speed bottleneck there.

    If your eye could pick up 13ms, you would see your old CRT screen like waved something with bad colouring and light intensity would go up and down like if you were turning your light in room on and off.

    It's very much same with watching movies - it seems fluent to you. You don't watch series of photos with sound (like you would if you had 13ms nerves), but movement. What everybody recognises as fluent movement is just and only your brain interpolating between two static frames it received through optical nerve... that's the reason all the videos are in about 25FPS (40ms) frame rate. Simply because human doesn't need more because human can't recognise more. Whoever says otherwise is either E.T. or lies to his own pocket. The hard cap of eye nerve bandwidth simply doesn't allow that.
  • mczak - Thursday, December 18, 2008 - link

    LCD screens do not lose any part of intensity whatsoever over time - unless you'd count backlight flicker (which is afaik several kHz)... Reply
  • JarredWalton - Thursday, December 18, 2008 - link

    I can tell you from experience that you will certainly notice the 40ms lag on some monitors; I don't have a problem with 20ms models, but the 2408WFP, Samsung 245T, and several other LCDs are perceptibly slower. You can't *see* it looking at things side by side, but use it and you can feel the lag. Even in using Windows, the mouse just feels like its sluggish and unresponsive. Gaming is even worse at times, depending on the game and how competitive you are.

    I didn't think it was a problem either, until I got a few truly laggy displays and did further testing. For a while I actually just thought the lag was the cheap Dell mouse I had connected to a test system, and then when I tested one of the TN panels I suddenly realized that the mouse was fine. Basically it felt like I had a cheap wireless mouse where everything was imprecise.
  • HollyDOL - Thursday, December 18, 2008 - link

    Well, don't forget there is significant lag on computer side as well. It takes some msecs for the software to move the cursor as well... Effect acumulates with further lag on monitor and pain begins. The lag effect should be much more visible with linux systems due to their switching of kernel and user modes of cpu. Could be worth trying out. Reply

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