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First Look: How LG's first 'passive' 3D TV stacks up

Consumer Reports News: May 09, 2011 11:56 AM

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Ever since we heard that all of LG’s 3D LCD TVs would use “passive” 3D technology, we’ve wanted to get one in the labs and see how it compared to the only other passive 3D set we’ve tested so far, Vizio’s 65XVT3D Theater 3D model. Both companies’ passive 3D TVs employ a polarizing filter on the TV, enabling viewers to wear lightweight, inexpensive passive 3D glasses rather than the pricier, bulkier active-shutter eyewear required by so-called active 3D sets.

In particular, we wanted to check one of LG’s most unusual claims: That unlike the Vizio set, LG’s passive 3D TVs were capable of displaying true 1080p (1920x1080) resolution to each eye . That claim goes against our general understanding of the current passive polarization techniques, which typically cut vertical resolution in half. In 3D mode, these passive TVs essentially divide the display screen—and thus the 3D stereo image—into odd and even lines, each group having a different polarization. The matching polarization in the glasses then steers the odd lines to one eye and the even lines to the other eye, which means each eye only sees half the 1080-line vertical resolution (1920x540).

So how can LG claim 1080p resolution when each eye is forever blocked from seeing half the lines? For each single frame of incoming video, LG refreshes the image to each eye two times. For one eye, the first pass presents the odd lines of the 1080p image onto the odd line rows of the screen, followed by the even lines, which are also—and unusually—presented on the screen’s odd line rows (not on the even line rows).

While this method technically presents each eye with all the 1080p information, it does so by placing half the lines of video in the wrong row location, at odds with standard video processing practices. Since the odd and even line information is presented sequentially to each eye, but in the same line locations, at any given time each eye is still only seeing half the resolution. But we’ll reserve final judgment for our resolution tests, which are presented below.

In the lab
For our evaluation, we purchased a 47-inch model in LG’s LW5600-series Cinema 3D TV. The 47LW5600, priced at about $1,700, is a fairly high-end Smart TV with a lot of features, including an edge LED backlight with local dimming, 120Hz technology, built-in Wi-Fi, and of course 3D capability. It also has a 2D-to 3D conversion feature, and like the Vizio set, it comes with four sets of passive 3D glasses.

We tested the set with several 3D movies, including Monsters vs. Aliens and Avatar, as well as with Panasonic’s 3D test disc. We also used special 3D test patterns we created ourselves to measure crosstalk, or ghosting, which occurs when images for the left and right eye aren’t kept completely separate.

There were several things we liked. One was the brightness of the set, probably even a bit brighter than the Vizio passive 3D TV, the brightest 3D TV we’ve tested to date. Also, the aliasing artifacts we saw on the Vizio—diagonal lines that looked jagged and moiré—were less pronounced on the LG set, though visible.

The Vizio set was remarkably free from ghosting except at very wide viewing angles. With the LG TV, as long as the viewer remained at eye level with the center of the set, crosstalk was also negligible across a wide viewing angle. Ghosting on the LG was most dependent on both the viewer’s vertical viewing angle and proximity to the set (which can alter the vertical viewing angle). In fact, the LG set appeared to be more sensitive to the vertical viewing angle than the Vizio, although the difference in screen size—47 inches diagonal compared to the Vizio’s 65-inch screen—could account for some of the difference.

Still, under normal viewing conditions, it is more difficult to make ghosting apparent on the Vizio whether viewing from below or from the sides or walking closer to the TV. (When we stood on a step stool and looked down at the Vizio, there was also an increase in ghosting, but Vizio’s screen is so large that in normal use a viewer would not likely encounter this viewing condition.)

Left: a 3D image viewed without glasses on the LG set; right: the same image viewed through 3D glasses shows noticeable ghosting and visible horizontal bands. (Photo taken at closer-than-normal viewing distance.)

We also noticed an unusual visual artifact on the LG set’s 3D mode: Non-uniform brightness variations in the form of bands running across the screens. These appeared as we approached the screen, first becoming visible at about a 6-foot distance. The bands can become quite apparent as you approach the TV, and appear also to be related to the relatively limited vertical viewing angle. The presence of both banding and ghosting increases as the viewer watches from above or below center of screen, and is most visible against a uniform background, such as a blue sky (see photo above). Our guess is that the bands are related to some interference involving the polarizers, but we’re not certain, and we did not see anything like this on the Vizio set.


1080p resolution—really?
We found that despite its claims, the LG LW5600 wasn’t able to produce true 1080p images to each eye in the 3D mode. The loss of resolution was apparent on our resolution test patterns, as well as on regular programming, where we saw course, jagged edges on objects that should have been smooth, and on broken lines that should have appeared continuous. It was especially visible on graphics and text, where we could see scan lines (see photo above). But on natural video (people, nature scenes), the lack of resolution and related artifacts were less apparent and never distracting.

In general, image artifacts caused by the lack of vertical resolution are definitely less pronounced on the LG than on the Vizio, whose jaggies and coarse edges are very prominent on most content. But it didn’t produce the clean, crisp edges we expect from true 1080p images, such as those we’ve seen on the best active 3D sets.

It should be noted again, however, that the ghosting and banding issues we’ve mentioned disappear when the TV is within the appropriate vertical viewing angle and proximity limits of the LG. Our initial evaluation leads us to believe that the LG set has a better overall image quality than the Vizio, thanks to the reduced coarseness in the resolution. But in 3D mode the LG does not provide 1080p resolution, though it may be good enough for all but the most discerning viewers.

Active or passive?
The natural question, of course, is which 3D TV technology—active or passive— is best? Now that we’ve been able to test two passive 3D TVs, it’s clear they offer a credible alternative to active 3D sets. Finicky viewers will likely opt for the extra detail, wide viewing angles, and ghost-free images offered by active plasma 3D TVs, especially on the bigger screens. But the 3D images on these TVs tend to be dimmer, and they require more expensive active 3D glasses.

For more casual viewers and families, passive 3D TVs may offer a reasonable compromise, trading higher resolution and some viewing angle issues in exchange for a brighter picture and cheaper, more comfortable 3D glasses. (And all the passive 3D TVs we’ve seen come with four free pairs, so you may not even need to get more.)

If you’ve decided to step up to 3D TV this year, let us know which of the technologies you find most appealing, and why. And of course we’ll continue to test more 3D sets of both types as they’re released.

Additional reporting by Claudio Ciacci; photos by Terry Sulllivan.

James K. Willcox

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