Tests point to extent of loss in Panasonic plasma black-level performance

Update April 2, 2010: Long-term testing shows similar loss of black level performance in two other Panasonic plasmas tested by CNET. Click here for details.

Panasonic has confirmed that its plasma TVs reproduce brighter black levels by design as they age, but will not divulge exactly how much brighter after how long. New testing conducted by CNET provides some hints.

Results from two aged Panasonic plasma TVs purchased in 2009 indeed show brighter blacks, and correspondingly reduced picture quality, compared with similar 2009 models with fewer hours.

The two aged TVs were a TC-P50G10 owned by CNET Senior Editor John Falcone and a TC-P42G10 loaned to us by CNET reader Efrain Perez. Both had approximately 1,500 hours of use, which at the average rate of 5.2 hours per day works out to about 9.6 months of age, at the time testing was conducted. We also measured another 50-inch TC-P50G10 and a 50-inch TC-P50V10, each with about 500 hours.

According to our measurements, the models with 1,500 hours both reproduced black at 0.023 footlamberts; the 500-hour models measured 0.008.

In an attempt to corroborate the measurements with real-world material, we conducted a side-by-side viewing session, attended by CNET staff and otherwise modeled after our standard TV test procedure, that pitted Efrain's TV against the 50-inch V10. When we originally compared a G10 with the V10 in 2009, using new review samples, we called their black level performance "basically the same."

That wasn't the case this time around. In dark scenes from "The Dark Knight" on Blu-ray, the 500-hour V10 clearly displayed a darker shade of black than the 1,500-hour G10, leading to more-realistic reproduction of nighttime city-scapes in Chapters 2 and 8, for example, the rooftop parlay in Chapter 8, and the silhouette of Bruce Wayne as he enters the room in Chapter 18. The difference was also visible in letterbox bars, albeit less so, in numerous brighter scenes. This viewing session was conducted with each TV set to the default THX picture mode, with no adjustments made to any picture settings.

Questions linger
The differences we observed and measured could be the result of what the company calls the normal aging process. According to Panasonic's statement, made after we first reported user complaints about this issue: "...Panasonic Viera plasma HDTVs incorporate an automatic control, which adjusts an internal driving voltage at predetermined intervals of operational hours. As a result of this automatic voltage adjustment, background brightness will increase from its initial value."

For what it's worth, however, these increases in black level performance over time don't seem normal in our experience. I haven't noticed any sudden change in black level on my 2005 Panasonic at home, for example, and a Pioneer Kuro we've used as a reference since September 2008 shows no increase.

Unfortunately we're still not sure about the true extent of the loss in black level performance. The sample size involved in our test is still quite small among the thousands of Panasonic plasma TVs sold last year. In addition, we have yet to observe or measure any substantial change in the models we're testing. The only way to know for sure how these TVs change as they age is to conduct a long-term test using more samples, something that's currently beyond CNET's resources.

We contacted Panasonic with these test results but the company declined to comment because of pending litigation related to the issue.

In the past the company claimed in response to our questions that the proprietary information regarding specific hour counts is a trade secret, and that black level performance is difficult to measure. In our experience, however, it's relatively simple to get consistent results (see our procedure below).

'But really, will I notice the difference?'
Panasonic also claims that "Customer satisfaction with our Viera Plasma's has been excellent. We are confident that the long-term black level performance will continue to provide customers with an excellent picture over years of use."

But in Efrain's case at least, customer satisfaction is not excellent. He tells us he first noticed the change himself "around late December/early January while I was watching 'Blade Runner' in the dark." He hadn't yet read about the issue on CNET, and had never previously visited AVS Forum where the first reports surfaced. He called the change "really noticeable and detrimental," and said he didn't agree with the characterization by Panasonic's Bob Perry calling it "subtle even among trained experts." Efrain does not consider himself a videophile or a video quality expert.

In an e-mail exchange he told us:

As for the TV's current performance, I am disappointed by it. Prior to purchasing the Panasonic G10, I owned a 2008 Samsung LN40A650 40-inch LCD, and I decided to switch to plasma because of the exceptional black levels and viewing angles it affords. When I first got the Panasonic, I loved it. The blacks were as deep as I have ever seen on a plasma outside of the Pioneer KURO. But now, to my eyes, the black levels on my G10 have diminished to the point that it looks more like my old Samsung when viewed from the "sweet spot" in the middle.

Efrain contacted Panasonic in late January and after getting nowhere with the company's customer service--the rep actually sent him Panasonic's original February 3 statement one day later--offered to send us his TV for testing.

Like other customers who have noticed the loss on black-level performance, many of whom posted comments to our stories, Efrain bought the TV expecting a certain level of picture quality. Like most of those customers and many CNET readers in general, he's evidently a tech enthusiast who weighs his buying decisions carefully.

So is John Falcone, and he didn't notice the change at all on his TV at home, which also measured the same elevated black levels. John says he rarely watches in a completely darkened room. Echoing his sentiments, numerous other commenters to our stories claim not to have noticed any increase.

Implications for reviews
Like many other picture quality characteristics, differences in black levels can be subtle and are highly dependent on room lighting, program material, and picture settings. In our TV reviews, however, we often have to compare between characteristics many viewers would call subtle. We consider black-level performance the most important aspect of picture quality, and Panasonic's 2009 plasma TVs scored as well as they did mainly because of their excellent black-level performance compared with other displays.

After seeing Efrain's TV compared with a V10, we feel justified in changing our evaluation of its black-level performance from "excellent" to "very good."

Whether the increase is noticed by everyone or even a majority of viewers, the results we measured on two different models, and saw in our side-by-side comparison, are enough to make us modify our reviews of all 2009 Panasonic plasma TVs accordingly (yet again). Their Performance scores will be reduced across the board by one point, bringing them more into line with the competition in light of their increased black levels.

How those black levels will hold up over the years to come is still an open question, one that only Panasonic can answer at this point. The company says its new 2010 models will incorporate a "more gradual change in black levels over time." We've been promised an early review sample of those TVs, and we'll call them as we see them--though the fact that these problems have taken hundreds of hours to manifest may call early impressions into question.

Black-level test methodology
Each Panasonic 2009 plasma television was measured using the following procedure. The TV was connected to a Sony PlayStation 3 via HDMI (settings) and set to THX picture mode. In the "Digital Video Essentials: HD Basics" Blu-ray disc, the 0 percent test pattern (under "Advanced Video Test Patterns") was then displayed onscreen and the player paused. The brightness control was adjusted until the outermost blacker-than-black bars on the pattern just disappeared (one more click of brightness upwards would make them reappear). Then TV would be set to its "scrolling bar" mode for 5 minutes to remove remaining image retention. After 1 minute displaying the 0 percent pattern, the middle of the screen was measured using the same Konica Minolta LS-100 luminance meter for all measurements, and the results, in footlamberts, reported above.