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Active vs. passive 3D: what's better?

If you buy a brand new TV these days, chances are if it's anything more than a bargain-bin model it will be able to play some form of 3D video. Almost all mid-range and high-end TVs from brands like Panasonic, Samsung, Sony, LG, Sharp and Toshiba support 3D playback, but different TVs use different methods to display the 3D effect. The two competing technologies are active 3D and passive 3D -- we're figuring out the major differences between them to decide which is better.

If you're picking out a new television and want to work out what's best for you, read through our LCD vs LED vs plasma TV buying guide.

Want to learn about 3D TV? Take a look at our 3D TV buying guide.

Active 3D is the technology that the first generation of 3D TVs debuted with, spearheaded by Samsung in 2010. Active 3D uses battery-powered 3D glasses which have LCD 'shutters' over each lens -- when 3D content is being shown, the LCD glasses darken to block the lens of each eye of the 3D glasses sequentially, in sync with the 3D TV itself. The 3D TV shows sequential frames of 3D footage to each eye -- because one glasses lens is blocked out, only particular video frames are shown to the right eye, and only particular frames are shown to the left eye. The frames shown to the left eye are shifted horizontally compared to the frames shown to the right eye; this horizontal shift is what makes video look 3D. Each frame contains a full 1080 lines in active 3D.

LG's new 'Cinema 3D' TVs use passive 3D. Passive 3D uses the same basic concept as active 3D -- the video frames shown to each eye are off-set against each other to produce a simulated 3D effect. However, passive 3D does not use any fancy technology in the glasses. Instead, each lens of the passive 3D glasses are polarised; the left lens is polarised oppositely to the right lens. It's complicated, but essentially each line of pixels on a passive 3D TV is polarised to only display video frames to either the left or the right eye of a pair of polarised 3D glasses; there are 1080 lines in a Full HD TV, so 540 for each eye.

There are advantages and disadvantages to both passive and active 3D -- the differences exist mostly in the glasses.

Passive 3D glasses are much, much cheaper than their active equivalent. Because they don't have any batteries, Bluetooth or complicated circuitry built in -- all they are is a pair of plastic frames and two polarised plastic lenses -- they are far more affordable, costing $19 for a bundle of two pairs from LG. You can buy polarised 3D glasses at the cinema for $1; though we assume the polarisation is different, it demonstrates the low production cost of passive glasses. In contrast, active shutter 3D glasses from the big brands like Panasonic, Sony and Samsung cost $100 or more, with premium models costing as much as $150. If you've got a dozen people coming around to watch a 3D movie, passive 3D is a clear winner in the price stakes.

Active 3D glasses are heavier than passive ones due to the battery and circuitry built in, as well as the thicker lenses needed to contain the LCD shutters. This hasn't been a problem during our testing, but if you're watching a 3D movie marathon active glasses might be marginally more uncomfortable. Passive 3D glasses also don't exhibit any 'flicker' -- if you've got particular kinds of lighting around your TV (fluorescent globes are the worst offenders), active 3D glasses can show the light as flickery due to the fast on-off effect of the active shutters built into the glasses. This is only a problem with particular kinds of lighting -- incandescent globes, for example, remain flicker-free in our experience.

To their credit, active shutter glasses are able to display more to each eye -- the alternating-frame technology means a full 1080p image is shown to each eye, rather than the half frame (alternating lines down the TV screen) that passive 3D shows. This means cleaner lines, especially on curves and edges shown on video. If high quality video is crucially important to you, active 3D is the choice to make. (You could just watch the movie not in 3D and have the best picture, but that's another story.)

So, passive 3D wins out on price, weight, size and anti-flickering, but active 3D is still the go-to for outright image quality.


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