60Hz vs. 120Hz vs. 240Hz - LCD Response Rate

 

Applications

By: Robert Wiley and Jack Burden

First, a note about why LCD TV manufacturers are attempting to increase the effective refresh rate (also called response rate) on their televisions. Well, it stands to reason that there would be no increase if there were not a problem of some sort to begin with. For instance, you never hear of plasma TV manufacturers claiming increased Hz rate technology.

Indeed there is a problem – motion lag. Motion lag results when the images displayed on the screen are moving quickly, or in some cases panning side to side slowly. In the former, a subtle blur can be seen on the screen as the LCD TV frame rate conversion struggles to keep up with the speed of the programming content – sports action is a good example of this. In the second case, a jerky appearance called "judder" can appear as the LCD has a hard time accurately displaying the moving image even though it may be moving slowly. This results from a combination of the internal processing chips in the LCD TV and the response rate of the TV.

So manufacturers are doing all they can to eliminate or lessen the effects of these problems. They have recently increased the refresh rate or response time to 120Hz and 240Hz as a premium feature on some of the newest high end LCD TVs. How much does it help?

It does a great deal to cut down on motion induced artifacts – especially with fast motion scenes. It decreases motion lag and judder. However, there are nasty side effects you should know about. When viewing film and broadcast programming in 120Hz/240Hz we see unwanted background noise introduced. Many of the tricks movie producers and programmers employ to create depth and give background information a background look are unraveled and what results is a distracting lack of depth. Cinematography is impaired. In some film reproduction, the background set becomes so clear that you can see the cheap tricks used in the studio to create an effect of say stones in the background. With 120Hz/240Hz you can see that they are plastic. It causes unnatural appearance of the image popping out of the background especially in when foreground characters are moving slowly.

You might think this increase in detail of background information is a good thing, but it gives the content a kitschy, plastic, cardboard cutout look that is very unappealing. This is why we only recommend using the 120Hz/240Hz feature for sports programming and gaming where the increased information works to the viewers advantage. Thankfully, thus far manufacturers have introduced the 120Hz/240Hz feature as an option that can be turned off and on (though not with a discrete button on the remote control). In our recent reviews of the Samsung LN-52A850, the LG 47LH55, and the Samsung UN55B8000 we note instructions on how to turn the 120Hz/240Hz features off.

Recently, manufacturers have introduced a 240Hz specification on some LCD TVs - some of which use the LED backlight manipulation as a mechanism which will produce an "effective" 240Hz "appearance" and others which state a straight out true 240Hz refresh rate. Some manufacturers TV models may claim "240Hz performance" and others 240Hz refresh rate. From our recent experience, a higher Hz rate in the panel produces a picture with less motion artifacts during fast motion and side to side pannning. 120Hz has less motion artifacts, lag, and judder than 60Hz, and 240Hz has less of the same than 120Hz. It's a marginal, not revolutionary improvement. In the end, these new specifications in performance allow the LCD manufacturers to mark up the product more while providing a new feature which is there essentially to make up for a serious flaw with LCD technology. It's the newest and greatest feature to convince you to upgrade. But consider beforehand how much sports programming and gaming you view when considering whether the feature is worth extra - especially in light of the need to turn it off for a majority of viewed programming.