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Active 3D vs Passive 3D

Which technology works best?

2010 was supposed to be the Year of the 3D TV. By now everyone was supposed to be watching everything from football to Britain's got Talent in three glorious dimensions. And it sounded great - until people discovered that the early active-shutter glasses were prohibitively expensive, and often hard to use for prolonged periods of time.

The new wave of 3D TVs coming in from LG and Vizio, however, work with 'passive' (polarised) 3D glasses, like the kind found in cinemas, which are cheaper and easier to use - but sacrifice image quality. So we decided to set up three 3D sets - a Sharp LC-60LE835U active-shutter 3D set, an LG 47LW6500 passive 3D set and a Vizio XVT3D650SV passive 3D set - side by side to see the differences for ourselves.

How 3D TV works

If you want to see a 3D image in a 2D plane (on your HDTV), you need a way to show your eyes slightly different images - that's how you 'trick' your brain into perceiving depth. The easiest way to do this is to wear glasses that can help to present a different image to each eye. (Smaller displays, such as the one found on the Nintendo 3DS, don't need glasses because the display itself is designed to show each eye a slightly different image, but this technology doesn't work well enough for larger displays quite yet.)

Active-shutter glasses are actually small LCD screens that alternately dim the left and right 'lenses' in succession. They rely on an infrared signal emitter in the TV that tells each pair of glasses when they should dim each lens, so each eye can see the image intended for it.

Since active-shutter glasses are fairly complicated electronics, they're pricey: a typical pair usually runs about £100, and works only on 3D TVs made by the same manufacturer. They depend on batteries to keep running, too. What's more, they're pretty heavy, especially if you're already wearing prescription spectacles - which can make watching a whole movie somewhat uncomfortable.

Passive 3D glasses, on the other hand, are sort of like a pair of specially designed polarised sunglasses. Unlike sunglasses, which are designed to block light equally from both eyes, polarised 3D glasses block different kinds of light from each eye, creating the illusion of depth. That means you don't need any kind of expensive, delicate electronics in the glasses themselves, nor do you need a proprietary infrared emitter to sync with the glasses - but since each lens is blocking out light, you're technically not getting a full 1080p image for each eye, though your brain should be perceiving a 1080p image when it puts the two together.

NEXT PAGE: Our test results

  1. Which technology works best?
  2. Our test results
  3. Tim's take
  4. The verdict

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