Active vs. Passive 3D

Buying a 3D HDTV today means choosing between two different types of 3D technology. Which is the better way to watch?

Glasses-free 3D is still a long way off, so if you want to watch 3D at home today, you need to choose between two types of 3D HDTV, along with two different flavors of 3D glasses. Active shutter glasses use electronic shutters to sync the eyes to two different pictures on the screen to create a 3D effect. Passive glasses use polarized lenses to separate the pictures to direct them to each eye. Each has its advantages and weaknesses, which we'll outline below to help determine which 3D technology is right for you.

Until recently, HDTV makers have typically stuck to a single type of 3D technology, and for almost all, it was active 3D. But that's changing. Manufacturers are still experimenting with 3D technology, and that will mean more passive 3D displays, and possibly even glasses-free 3D HDTVs in the not-so-near future. Panasonic debuted its first passive 3D HDTV this year while still offering active 3D sets, while Sony is rumored to be working on its own passive screens, despite the fact that most Bravia televisions (and the PlayStation 3D Display) use active 3D.

Active Shutter 3D SystemsHDTVs manufacturers that currently sell active shutter 3D HDTVs: Mitsubishi, Panasonic, Samsung, Sharp, and Sony

Active 3D uses glasses with electronic shutters that flicker (it's too fast to be noticed by the human eye) in time with the display to separate the picture into two. The screen rapidly shows two pictures, and a built-in infrared emitter or radio transmitter tells the glasses how fast they have to shutter to make sure the right picture goes into the right eye. Each image is delivered to a different eye, giving the effect of depth. The glasses are electronic, so they tend to be bulkier, less comfortable, and more expensive than passive-lens glasses. And they require power, so you'll have to make sure they're charged up before your 3D movie screenings.

Sometimes, you'll find active 3D glasses in the box with your HDTV, but often you won't. Most active shutter 3D glasses retail for between $50 and $120 per pair, which can really add up if you have a large family that wants to watch Avatar together. Recently, however, Samsung released a $20 pair, which could signal a new wave of affordable active shutter glasses. Two pairs (for the LED 6500 Series) or four pairs (for the LED 8000 Series) are included with the company's high-end 3D HDTVs, making Samsung currently the most economical option for active 3D. Other brands, like Sony, Panasonic, and Mitsubishi, typically don't include glasses.

While active 3D is less convenient than passive 3D, it generally offers a better 3D picture. Content tends to "pop" more effectively, displaying more depth and producing a more compelling 3D effect. Because the lenses synchronize with the display to make sure each eye is seeing the right picture, active 3D screens tend to show less crosstalk (that "ghosting" effect that shows part of the opposing 3D picture to the wrong eye). Active 3D displays are also easier to watch off-axis from the center of the screen, which means a better experience for everyone if you have multiple viewers.

Passive 3D SystemsHDTVs manufacturers that currently sell passive 3D HDTVs: LG, Panasonic, and Vizio

Passive 3D uses glasses with special polarized lenses that filter images to each eye to produce a 3D effect. The two pictures are shown superimposed on each other, with a filter on the screen to make the two pictures distinct. The filters in the glasses then make sure each eye only sees the picture it's supposed to. Because the glasses don't have any electronics or need any power, they're very light and inexpensive.

Most passive 3D HDTVs come with several pairs of glasses, and you can buy more online for a few bucks a pair. Also, the glasses are also easier to use because they don't require a connection (either infrared or radio) to the TV to work. Vizio and LG offer the most economical options, as their passive 3D HDTVs come with several pairs of glasses, so you can supply a large family with what they need for 3D content watching without paying extra.

Passive 3D is more convenient, but it's not perfect. Passive sets tend to deliver a less-pronounced 3D effect than active HDTVs; the picture shows three-dimensional depth, but images don't quite "pop" the way they do with active 3D. Passive 3D also tends to show more crosstalk, especially if the viewer turns his head or sits off-axis from the center of the screen.

Glasses-Free 3D SystemsHDTVs manufacturers that currently sell 3D HDTVs that don't require glasses: None

Several companies, including Sony and Toshiba, have promoted glasses-free 3D for HDTVs as a future technology, but it hasn't yet come to fruition. This technology uses a filter on the screen itself to separate the images, like, say, a lenticular comic book cover. If you look at the display from the right angle, the right pictures will hit the right eye, without needing glasses to separate them. But from what we've seen so far in trade-show demos, the technology is nowhere near ready for prime time. The Nintendo 3DS portable gaming system employs this technology to modest success, but it's currently unavailable on larger screens. If you want to try the technology, the Nintendo 3DS offers the same concept on a much smaller scale.

Which 3D Is Best for You?

Active 3D generally offers the best picture, but right now, passive 3D is more convenient and affordable. Even though active shutter glasses are becoming less expensive, you still have to deal with the bulk and the inconvenience of keeping them charged. Having said that, we've seen some very convincing 3D from passive screens like the Editors' Choice Vizio M3D550KD, but it usually comes down to whether you want to spend more money for a higher-quality 3D effect. You should consider how much 3D content you'll be watching, and the number of viewers you'll typically have watching at a time, and make your decision accordingly.