Wednesday, December 22, 2010

Contrast Ratio, Response Time, Refresh Rate

There are some specifications for LCD TV which potential buyers may want to compare but find confusing. The two common ones are Contrast Ratio and Response Time or more commonly used now, the Refresh Rate. For Plasma TV, these are not issues since inherently Plasma TV are better than LCD TV in these two areas. The first one, Contrast Ratio, should be totally ignored as this is the one spec that is really useless and often misused by some manufacturers.

By definition, contrast ratio is the ratio between the brightest white and the darkest black a TV can display and you see figures ranging from 30,000:1 to the ridiculous 5,000,000:1 or even higher quoted by some manufacturers. Does it mean that the later is 500 times better than the earlier one? Definitely not.

Here are the reasons why you should not look at this Contrast Ratio at all. Firstly, manufacturers do not tell you how they come up with the figures as there is no standard agreement among manufactures on how this should be done so it is free for all in this area and some manufacturers keep on increasing this figures hoping to boost sales in the process. So it is pointless to compare figures between manufacturers. These figures are probably measured in a totally dark laboratory and once there is some ambient light where we put the HDTV, these figures go out the window. Secondly, our eyes can only differentiate contrast ratio of up to about 1,000:1 normally so anything above that, the difference is not noticeable unless you are a robot. These fantastic figures are measured for static images so it has no meaning when we watch movies on the TV.

Among manufacturers, LG seems to be quoting higher and higher contrast ratio figures while Toshiba is using a comparatively modest 50,000:1 for all their LCD TV. Samsung used to be like LG but now it does not quote figures but just uses terms like "high" and "ultra" (do not know what they mean but it does not matter). Not sure what other manufacturers are quoting but whatever figures they use, you can just ignore them. Contrast Ratio is not the only item that affect the quality of the picture and in any case, it makes no difference in the real world for watching movies.

(Plasma TV has better Contrast Ratio than LCD normally by virtue of the technology employed so there is less number games for this in Plasma TV specs.)

Another specification is harder to classify, that of Response Time. This figure used to be quoted frequently earlier (especially for gamers) but not so much now simply because the technology for improving the response time of LCD has more or less reached the limit. This item measures how fast an LCD pixel can change state so the smaller figure the better. This used to be in 10's of milliseconds but now it is like 5ms or down to 2ms for some models. Anything 5ms or below should be OK for normal use and in practice the difference is not very noticeable after that. A slow response time will result in motion lag, smearing or trailing effect for fast moving objects in action scenes or sports. (In reality, there is also no agreed standard on how this should be measured and quoted by manufacturers but for simplicity, we assume that this is done more or less similarly and the figures should be used just as a guide; anyway, the discrepancies are not as great as those seen in the Contrast Ratio figures.)

In order to improve the response time, manufacturer is now resorting to increase the refresh rate of the TV to give them another opportunity to play the number game of higher is better. The original refresh rate used is 50Hz (for PAL land like Europe and Malaysia) and 60 hz (for NTSC land like USA and Japan) and newer LCD TV have double or 4 times this to 100Hz or 200Hz (or the corresponding 120Hz and 240Hz for USA and other NTSC countries). The average human eye can discern the improvement from 50 Hz to 100 Hz (or 60 to 120Hz) but the next improvement to 200Hz (or 240Hz) may not be so apparent to some. The newer LED TV are pushing this even further to 400Hz (or 480Hz) but it is doubtful if the normal human eye can see the difference but it does help manufacturer to sell more of these TV sets and make a better profit. Manufacturers are using different terms for these higher refresh rates to attract customers, such as TrueMotion, MotionPlus, MotionFlow, Natural Motion, etc to give the impression that their technology will enable the HDTV to display smooth motion.

Each manufacturer uses a different technology to implement the higher refresh rates so results will be different and some are more effective then others. In addition, a lot depends on the source material itself so if it is bad, no amount of refresh rate will improve it and it may even show up the weakness more. Thus the increase from the standard refresh rate to the higher rates may or may not be a visible improvement for some brands. To really compare, you must play the same source material on two different sets and watch them side by side. If there is no noticeable improvement, go for the lower refresh rate model which is usually the cheaper one. Again, use your eyes as the judge.

In summary, you should totally ignore the Contrast Ratio figures. For the Refresh Rate, you can compare the figures from different manufacturer up to a point as a guide as higher figures are hard to discern visually in real life. This will also vary from model to model. The best is to use your eyes as the judge, not the figures produced by the manufacturers as they are there to impress and sell their products. A good image is not due to just one or two items of the specs but it is a complex mixture of many other factors.

In fact, a finely calibrated entry level HDTV will give a better viewing experience than a badly calibrated high end unit. As an analogy, a well-tuned Proton will perform better than a badly tuned BMW. OK, maybe this is stretching it a bit but I think you get the idea!

Ronald Kwok


  1. many thanks for these good infos..

  2. Thanks for all this information. I’m trying to educate myself on all the terminology and learn what all these specs really mean, so I can find the best TVs that I can. This article has been very helpful. Now that I’m getting a Hopper whole-home DVR installed, I want to upgrade my last two TVs to HD, since the Hopper will be sending all my HD channels to every room. A coworker at Dish recommended the Samsung, what do you think of that brand?

  3. Thanks for viewing. My view is that there is little practical difference among the major brands since the technology has now matured. It is more a matter of features that you want, the physical aesthetics, the after sales service, the price, etc. In the end, it is personal preference so let your eyes be the judge. The best TV is the one you enjoy watching!