In Praise of Plasma

I've always been a bit bummed that plasma TVs hold such a small market share compared with LCDs. And it doesn't help when companies like Vizio and Pioneer drop out of the plasma business altogether. Yet when I visit my local CostCo, I can see why—the LCDs on display are definitely brighter than the plasmas, which is why they fly off the shelves while the plasmas languish.

I bemoan this state of affairs because, in general, plasma looks better than LCD in many circumstances at home. Yes, LCD is better suited for bright-light environments—even outdoors—and technologies like LED local dimming and frame interpolation have improved LCD performance dramatically. But for a light-controlled home theater, I prefer plasma.

Panasonic recently reinforced this notion with a press briefing. Interestingly, the company makes both plasma and LCD TVs, but unlike others in both camps, such as Samsung and LG, Panasonic's lines do not overlap in size—it offers LCDs from 26 to 37 inches and plasmas from 42 all the way up to 103 inches. So it's really no surprise that Panasonic would advocate plasma over LCD for larger sizes.

The presentation was delivered by Isao Kawahara, Panasonic's chief plasma engineer. He started by pointing out that the best screen size depends on the seating distance, and based on various studies, that size is larger than most people think.

Kawahara claimed that the optimum horizontal viewing angle—the angle formed by the sides of the screen at the viewer's head—is 45 to 48 degrees, which translates to a seating distance of about twice the screen height (abbreviated 2H). According to this, the optimum seating distance for a 58-inch (diagonal) screen is less than five feet!

Sorry, but that's a bit too close for me. First of all, he based his calculations in part on where people tend to gravitate if they're the first ones to find their seats in a commercial cinema—about 2/3 of the way back from the screen. Of course, that image has an aspect ratio of 1.85:1 or 2.35:1, not 1.78:1 as with an HDTV. Also, the SMPTE spec for viewing angle is 30 degrees, while THX recommends an angle of 40 degrees, which translate to a seating distance of 3.3H and 2.4H, respectively, or 7.9 and 5.8 feet for a 58-inch (diagonal) screen.

Kawahara pointed out that, at less than 2H, most viewers can see individual pixels, while at more than 3H, they start to lose detail, so I think a seating distance of 3H (or 1.47 times the screen's diagonal measurement) is just about right. Even then, you need a bigger screen than most people realize—for example, 58 inches (diagonal) for a seating distance of about seven feet.

Next, Kawahara noted that the contrast of an LCD flat panel drops dramatically beyond about 20 degrees off axis, and colors start to shift unevenly as well, as seen in the photos at the top of this blog (plasma on and off axis above, LCD below). If we accept his recommended viewing angle, that means the edges of the image on a large LCD at the specified distance will lose contrast and color fidelity, even if you're sitting dead center, because the edges are 24 degrees to either side. An interesting idea, but I've never noticed this problem when watching a large LCD—maybe I haven't been close enough!

Other topics included LED backlighting with local dimming, which lowers the black level and raises the apparent contrast of LCD TVs with this feature. However, the LEDs are grouped into relatively large zones, which leads to haloing around small, bright objects on a dark background. By contrast, plasmas control the brightness of each pixel individually, so there is no haloing. I had to agree with him on this one.

I also had to agree that plasmas tend to exhibit much better motion resolution than LCDs, even those with 120Hz or 240Hz frame interpolation. Those higher rates do sharpen objects in motion, but they can induce artifacts of their own, and the process imparts a "video look" that many viewers hate. In a side-by-side comparison of the same material on a plasma and 240Hz LCD, objects in motion looked much sharper on the plasma than they did on the LCD (which had frame interpolation enabled—I checked).

The biggest surprise for me was the claim that plasmas with an Energy Star 3.0 rating consume no more power on average than an equivalent LCD with the same rating. In fact, we saw data that showed many LCDs with that rating consume more power than some plasmas of the same size. The key words here are "on average"—LCDs consume a relatively constant amount of power over time, whereas plasmas consume more or less power depending on how bright the overall picture is at any given moment, which is taken into account in the Energy Star testing.

For the most part, Kawahara was preaching to the choir with me, though I don't subscribe to his screen-size recommendations. I've always said that I prefer plasma for a large-screen home theater because of its better motion detail, generally lower black level, and better off-axis image quality. LCDs are trying to compensate for the first two issues with frame interpolation and LED backlighting, respectively, and these technologies can improve LCD performance a lot. But they are not perfect solutions, and there's not much that can be done about off-axis performance.

If Energy Star 3.0 plasmas consume no more power on average than equivalent LCDs, that removes one of the last advantages enjoyed by LCDs. The only ones left are a typically matte screen and more raw light output, making them look more eye-catching in a retail showroom and better able to withstand lots of ambient light at home. But if you can control the light in your room and want the best possible theatrical experience with a flat panel, plasma is the way to go in my book.

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