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Video: High refresh rates in LCD TVs


Steve, Crutchfield TV expert, explains what LCD TV refresh rates really mean, and how refresh rates higher than 240Hz are achieved with backlight scanning. Find out if a TV with a high refresh rate is right for you.

Steve: If you've been looking at LCD TVs you've probably seen a lot of references to higher refresh rates like 120Hz or 240Hz or even higher. And what higher refresh rates do is try to reduce motion blur which can be a problem with LCD TVs. And different TV makers have different names for this technology. Sony calls theirs Motionflow. Samsung calls theirs Auto Motion Plus. But it's all basically the same technology.

So what is the purpose of these higher refresh rates? Well it's to make the video look smoother. The standard refresh rate, or frame rate for video, is 60Hz, or 60 frames per second. And that's the rate that you get from video sources like your Blu-ray player or your cable box, and that's the display rate of basic LCD TVs. When you have TVs that have a higher refresh rate they're actually repeating the image more frequently so that the image looks smoother on screen so that, for instance, a 120Hz TV is actually creating one new frame for each actual frame. And then a 240Hz TV is creating three new frames for each actual frame. And when it adds these new frames, it inserts them into the video stream and adds motion compensation so that it all looks very smooth and natural and it gets rid of the motion blur.

So right now the fastest actual refresh rate that you'll find in a TV is 240Hz, but you will see TVs advertised with higher rates like 480Hz, even all the way up to 960Hz, and that's where it can get a little confusing. So let me just explain that.

What's happening with those higher refresh rates is actually a different process. It's called backlight scanning. And what happens there is the TV's LED backlight actually flashes, or blinks, at really high speed and that is synchronized with the screen's refresh rate to further reduce the amount of time each image is flashed onscreen. So the end result is that the image looks just that much smoother and clearer, and so that technology is great if you like, watch a lot of fast action sports. But a lot of people find, including me, that these refresh rates aren't so great for watching movies. They can make them look unnatural and kind of flat and video like. But luckily most TVs let you go into the menu and adjust the amount of motion blur and judder reduction that's going on. So you can end up with movies that look film like the way they should.

So do you need a TV with a higher refresh rate? Well, if you watch a lot of sports it's a good idea because it really does make fast action look smoother. Also, if you're shopping for a 3D LCD TV you should probably get one that's at least 240Hz because when a TV's in 3D mode it actually splits the refresh rate because it needs to send two separate images to create the 3D effect. So, say a 240Hz TV is sending 120Hz video to each eye.

If you have any questions about refresh rates or any of the TVs that we sell just give us a call.

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