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How many “Hz” do I need? What refresh rate should I get?

When you are buying a new HDTV you will probably come across something called refresh rate that is measured in Hz. Now, do not get this confused with GHz in computers or MHz on radios. That is a completely different measurement.

Read “720i vs. 720p vs. 1080i vs. 1080p” to understand frame rate.

The refresh rate rating in HDTV stands for how many times will the TV draw the image you see from its source (DVD player, Blu-ray player, cable satellite…) and display it on the screen every second. So, if you have 60Hz TV it will display 60 frames every second. Most major picture movies are at 24 frames per second (fps) while most of the TV shows you watch are at 30fps. Reading this you are probably thinking that 60Hz HDTV is plenty since movies have only 24fps and TV shows have only 30fps. Yes, but no! If you have a 60Hz HDTV and you are watching 24fps movie, 60 divided by 24 gives you 2.5 which is not a whole number. That means that the TV will display one frame 3 times and other will be displayed 2 times, and then it repeats. This is called a 2:3 pulldown. Some people are sensitive enough that they will see this 2:3 pulldown inform of flickering image, which can cause headaches. With 120Hz HDTV’s, 120 divided by 24 is 5 and 120 divided by 30 is 4, so there will not be any pulldown for movies or TV shows.

Hz (Refresh Rate) in 3-D HDTV’s

What you read above describes how non 3-D HDTV’s operate. The 3-D HDTV’s operate in same fashion, but everything is doubled. 3-D movies are in at least 48fps, while other 3-D material is in at least 60fps. It is because each eye is technically watching a full movie from slightly different angle, which your brain interprets as 3D image (read more about 3D). In this case, for same reasons as in non-3D HDTV’s, 240Hz will give you best results in all cases with no pulldown. Anything above 240Hz does not divide nicely into both 48fps and 60fps.

So how many Hz do you actually need?

In non 3D HDTV’s 120Hz is absolutely enough. Anything above that is just inflation by manufacturers to make their TV’s seem better that the competitors. In 3D HDTV’s get 240hz, but not more.

example of hz

Personal Observations:

I have a non 3D HDTV that is rated at 600Hz and I must say that I love it. The picture is phenomenal, assuming you have true HD source.


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