THE BIG PICTURE

It's been a bad week for Panasonic. A report of suddenly rising black levels in its 2008 and '09 plasmas gained some serious traction throughout the A/V community over the past few days, even though it's been brewing since July 31, 2009, when AVS Forum member Orta (who I assume is male) posted that his TC-P50G10 doubled its black level literally overnight, with measurements to prove it. As you might imagine, this led to a flurry of concern, to which Panasonic finally responded with this official statement:

Panasonic Viera plasma HDTVs deliver exceptional picture performance throughout the lifetime of these products. Various elements and material characteristics of all electronic displays change with use over time. In order to achieve the optimal picture performance throughout the life of the set, 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. After several years of typical use, the internal material characteristics will stabilize and no additional automatic voltage adjustments are required. The Black Level at this stabilized point will yield excellent picture performance.

The newest Viera plasma HDTVs incorporate an improved automatic control which applies the voltage adjustments in smaller increments. This results in a more gradual change in the Black Level over time.

Okay, so Panasonic plasmas are programmed to increase the "background brightness" (i.e., black level) to compensate for normal aging in the first few years of normal use, after which it should stabilize. But are they really supposed to suddenly double the black level at some point? If so—or even if the increment is supposed to be smaller than that—can the firmware be updated to minimize this effect? Maybe not—according to a cnet report, Bob Perry, a senior VP at Panasonic, says that the TVs work as designed, so there's nothing to fix.

This leads me to wonder if a programmed increase of driving voltage and thus black level over time is common practice among all plasma manufacturers. According to one of my tech contacts at Samsung, he's not aware that his company's plasmas change their level over time. I've also asked LG the same question about its plasmas, but I didn't receive a response by the time I posted this blog.

I applaud AVS Forum member Bdemers for collecting and graphing data about this issue from other members; the graph is reproduced above with permission. I question the absolute precision of these measurements, since most seem to have been taken with relatively inexpensive colorimeters that are probably not accurate at very low light levels, and the conditions under which the measurements were taken are probably inconsistent from one user to the next. But assuming that the measurements of each TV were taken with the same device under the same conditions, the results are valuable as a relative indication of how a given set's black level behaves over time.

As you can see in the graph, the black level of most entries did rise over time. But notice that, in at least one case, the black level did not rise, which corresponds to reports from some Panasonic owners of no visible increase in black level after hundreds of even thousands of hours of use.

This whole thing is particularly troubling to me as a reviewer, since I don't normally have the opportunity to test any TV over a long period of time. Even worse, the problem seems to be inconsistent, so I might or might not see it even if I could run a review unit for hundreds or thousands of hours. All I can do is report what I find, both good and bad, while setting up and watching each TV during the time I have with it.

Clearly, there are anecdotal indications that Panasonic plasmas increase their black level over time—the company even admits it—but there's no proof that it's universally problematic. I tend to think that a sudden doubling of black level is an isolated defect, not an endemic problem, since not all Panasonic owners report it. Also, while the AVS data are interesting, they do not form a statistically significant sample, and AVS members are more likely than the general public to notice and report even a slight increase in black level.

So for now, I'm not going to renounce my overall opinion that Panasonic plasmas are among the best you can buy today. However, I'm also going to keep an eye on this evolving story, and I'll report any significant developments. If you've seen rising black levels in your Panasonic plasma—or not—please let your fellow UAV readers and me know by posting a comment here.