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LCD HDTV Refresh rate: 60 Hz vs. 120 Hz

December 23rd, 2010 Leave a comment Go to comments

HDTV Screen refresh rate is the unfamiliar term for most of the TV consumers. To grasp this area, we can begin with the basic concept. Suppose I have a computer or TV screen with negligible refresh rate. What will happen when I play a movie? The screen will not clear the previous images as fast as needed, which is essential to display the next coming images on the sequence. In simple words without any jargons, suppose you’re drawing on a black board. You need to delete the contents on it to draw the next. This is the same thing needed for the complex display technologies to display fast moving objects and sports event videos. If the refresh rate is not enough the parts of previous image will retain on the screen giving a jerked or polluted image with artifacts. This is commonly called ‘judder effect’ by Industry experts.

Refresh rate is usually expressed in frequency unit Hertz. This means how many times the TV screen rebuilds the screen contents or image sequence in a movie. Films usually have 24 frames per second (fps). This means 24 images creates one second video content. A 60Hz LCD HDTV converts this frame rate to 30fps before feeding the signal to the display. Then each image in 30 fps is reconstructed twice in 60Hz screen. Converting 24fps to 30fps is known as 3:2 pull down. The failure in doing this process with full efficiency can cause judder effect with jerky movements on the screen.

Which is better (60Hz or 120Hz)?

In light of the technical facts connected with the film producing standards, we can say a 120Hz refresh rate is much better in viewing a film or fast moving objects on the screen. This is because the 120Hz display repeats 24fps five times in a second. The value of exact multiple eliminates the need for a 3:2 pull down as in the case of 60Hz screen. So the judder effect will not occur in 120Hz screen. But, now 240Hz and more are available in market. This will repeat images 10 times in a second. Usually 120Hz is enough. There is not much clear cut difference in performance between 120Hz and 240Hz or higher refresh rate LCD HDTV. So the only thing is an extra 200$ escapes from your pocket.

The refresh rate technology fights with the motion blur effectively. But most of the main stream manufacturer’s trials other shortcut ways to achieve high quality display for fast moving objects. Sony experiments their models with clear option for a soothing effect. Some use repeated backlight firing to eliminate the motion blur created while viewing sports events.

A higher value of refresh rate is always desirable to deal with contents in full of motion. The difference between higher and lower refresh rate can be better explained by the experienced users. For example while playing PC racing games with an LCD TV screen with computer connectivity and higher refresh rate, the fast moving contents with respects to the static screen objects creates an interesting experience of perfection and reality.

Key Facts

– Moving from 60 Hz to 120 Hz gives some definite advantage.
– Moving from 120 Hz to 240 Hz does not seem to benefit as much as from 60 Hz to 120 Hz
– Fast moving scenes are benefited the most with higher refresh rate.
– Higher refresh rates of 120 Hz / 240 Hz also introduce some background noise.
– Some TVs also has a feature to turn off the 120 Hz or 240 Hz refresh rate.

Other facts you may want to know when planning to buy an HDTV ?

– The truth behind the HDTV Contrast Ratio.

1080p Vs 720p resolution

– HDTV Buying Guide – Article coming soon on Starred Reviews.

The LED HDTV – the backlight – Article coming soon on Starred Reviews.

– Historical fact – LCD TV Vs older CRT Monitor.

  1. September 14th, 2014 at 21:00 | #1

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