Active 3D vs Passive 3D
By Steve Morris, 26 Nov 2012
Active vs passive
If you're choosing a 3D TV, you're going to have to decide between active 3D and passive 3D. That's not easy. There are competing and confusing claims on both sides and there's no clear winner. Here we're taking a look at both to help you make an informed decision.
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With active shutter 3D glasses, the system favoured by Samsung, the 3D glasses are active, which means that they allow light into the left and right eyes alternately, using a liquid crystal layer in the glass that opens and closes rapidly. This enables each eye to see a slightly different image, and creates the perception of depth. The glasses operate at 60 frames per second or faster, synchronised with the TV.
Active 3D glasses are expensive, so you'd expect there to be a significant advantage in using this method. The main advantage claimed is:
- Full 1080p HD viewing.
But there are problems with active 3D glasses:
- The glasses are expensive, so kitting out a whole family can be very costly.
- The glasses are quite heavy and can be uncomfortable to wear for long periods.
- The shuttering effect of the glasses can result in a flickering effect.
- Because the light to the eye is blocked half the time, the brightness of the perceived image is reduced by half. It's like watching TV while wearing sunglasses.
- If the TV's refresh rate is too slow (200Hz or less), you get "crosstalk", meaning that the left eye sees the ghost of images intended for the right eye, and vice versa.
After reading the disadvantages of active 3D glasses, you're probably thinking that passive is the better option. But it's not going to be that simple. Let's take a closer look.
With passive 3D, the glasses are similar to ordinary glasses, but the left and right glass is polarised differently. This means that each eye sees a different image, creating the 3D effect. The glasses are very simple and cheap to make and this gives the technology some obvious advantages:
- The glasses are cheap, so you can buy enough for the whole family and friends.
- The glasses are light and comfortable to wear.
- There's no flickering effect.
- Images are much brighter than with active shutter glasses.
But there are disadvantages too. In order to display a different image to each eye simultaneously, half of the pixels in the TV are polarised for viewing by the left eye and half for the right eye. This is achieved by polarising alternate rows of pixels on the TV screen for left and right viewing. The result is that each eye sees only half the pixels on the screen, with alternate lines blacked out.
Supporters of passive 3D claim that the image is still full HD, because there are 1080 lines in total, but critics say that it is only half HD, because each eye sees only half a HD image. Perhaps more to the point is the fact that on a big screen you can actually see this pattern of black lines or the interference patterns they produce. This will be more noticeable when watching 720p broadcast TV (e.g. Sky 3D) then watching 1080p Blu-Ray.
In this article, I've presented the arguments for and against each kind of technology. While I'd like to give you a clear answer about which is better, it's just not that simple.
If 3D is something you really care about, then you need to view each type of display yourself and make your own decision.
Interestingly, the best-selling TVs tend to be from Samsung, and Samsung use active shutter technology for all their 3D TVs. On the other hand, LG turned its back on active shutter glasses and embraced passive 3D as the way forward, claiming that more than 80 per cent of people prefer watching passive 3D.
The jury's still out, but here at S21 we find ourselves leaning in favour of passive glasses. The interference patterns on passive 3D TVs can be avoided by sitting further away from the TV - something that's always a good idea when watching in 3D. With active 3D glasses, the flickering effect plus the weight of the glasses and the possibility of ghosting makes the experience less comfortable and less relaxing.
Finally, we should mention that all 3D plasma screens use active shutter technology. So, while we think that plasma screens are better than LED displays, we realise that passive 3D technology isn't available with plasma. You just can't have everything, it seems!
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Comment by Ogdenous from USA on 28th Nov 2012
Active glasses also cause more strain on the eye so maybe not good for those long movies or kids.