One of the most common questions we get here at TekSpree through our Facebook page or email service is "what are you wearing?" But, the second most common question is "What's the difference between 60hz, 120hz, and 240hz. And, why should I care?!" Well, I'm certainly glad you asked, because it's a fascinating question to those of us that love television. Much more interesting than what we're wearing - particularly since we always
answer customer questions in the nude.
We've come up with this handy dandy guide to Television Hertz.
First, it's important to understand that there are two processes involved in watching a movie on TV. The first is filming the show, and the second is displaying it. When a TV show (or movie) is filmed, a camera speed of 24 or 30 frames a second is used (depending on the camera). There are some variations between camera makers, but in general 24 or 30 frames per second is about right. As you know, technophiles love abbreviations, so 24 frames per second is usually shortened to 24fps. Every second of filming contains 24 (or 30) snap-shots that when viewed in succession give the illusion of movement. It's the same process that made your childhood flipbooks work (or for those that are older: the nickelodeon machines).
Now that we have the image recorded, we have to play it on a television screen. To do that, you must understand the second part of the television process: displaying the image. The speed at which a television can switch between one frame and another in one second is called the "refresh rate" and is measured by "hertz." If your LCD TV is capable of displaying only one image (or frame) every second, then it has 1hz capability. Congratulations, you have a very expensive digital photo frame. If you want to watch a movie, which is shot in 24fps, then your TV has to at least be capable of displaying 24 images per second. We also can say, it must be at least 24 hertz.
Why is this important?!
When you were watching a 24fps movie on a TV that's capable of displaying 24hz, everything was perfect. The TV you had was capable of displaying all 24 frames per second. If your movie was shot in 30 frames per second, and your television is only displaying 24 of those frames every second, you would be missing 6 frames of action - that would make the movie quite unwatchable! To solve this problem, TVs now come in at least 60hz to allow you to watch a movie shot in 30fps. At 60hz, every frame is displayed twice per second: 30 x 2 = 60.
What happens if you are watching a 24fps movie on a 60hz TV? Well, this is why hertz are important. 60 divided into 24 frames is 2.5 - not an even number. So, the image has to be manipulated somehow to make the 24 frames fit into a 60hz refresh rate. Usually this is done by inserting copies of 6 frames to increase the 24fps into 30 - which can now be displayed properly on a 60hz television. This process is referred to as interpolation
The problem is that whenever you manipulate the image on a TV, weird things happen. A side effect of adding frames through interpolation is that the movement of the show becomes unnaturally smooth (sometimes referred to as the "Soap Opera Effect"). To counter this problem, television makers started to release higher refresh rates: 120hz and 240hz.
The beauty of both the 120hz and the 240hz refresh rates is that both 24 and 30 can be divided into them evenly. If you are viewing a 24fps show on your 120hz television, each frame of the 24 will be displayed 5 times a second (24 x 5 = 120). If it's a 30fps show, then each frame is displayed 4 times a second (30 x 4 = 120). You can take out your TI-85 calculators now and do the math for the 240hz TVs. I'll wait....
Did you also discover that 24fps and 30fps can be evenly distributed into 240hz? Good... now go sell that TI85 on eBay, it's practically useless after high school!
Which is better, 120 or 240?
The only significant difference between the 120hz or 240hz systems will be in presenting 3D content. If you think you are going to be interested in viewing 3D movies and TV shows, then you should get a 240hz system. Why? Because 3D works by showing each of your eyes only half the image on the screen - this is what makes the image three dimensional and why you have to wear special glasses. Because of this halving, your 120hz TV is really only showing 60hz to each eye (and 24fps does not go into 60hz very well). If you have a 240hz TV, each eye gets 120hz and you'll be able to watch both 24 and 30fps shows without any image manipulation.
Does this really make a difference?
Television viewing is a lot like wine. Everyone has an opinion on how to enjoy it. In the end, the final judge should be yourself. Some people love to know they are watching the very best image quality. Others just can't bring themselves to pay the additional expense to have a 240hz TV. For this reason, I highly recommend buying your television from a local electronics store so you can see the image quality before it gets delivered to your house. Then, of course, go to TekSpree.com for your 3D glasses (and our nifty dust monster!)