The most recent results of measurements taken by CNET confirm that after a few hundred days of on time, the company's 2010 plasma TVs do lose some of their ability to produce a deep shade of black, which is a major factor in picture quality. Even after the loss, however, both can still achieve comparatively deep black levels, and according to Panasonic that shouldn't change significantly after an initial period.
We've been testing two 2010 models, the TC-P50VT25 and the TC-P50G20, since we received the review samples from Panasonic earlier this year, and until now we haven't measured any increase in the brightness of "black" (known as MLL, or Minimum Luminance Level).
However, after being run for what amounts a small fraction of their expected lifespans, each TV has shown an MLL increase. "Black" on the VT25 went from 0.004 to 0.007 footlamberts (ftl) after 1,543 total hours (the equivalent of 297 days at the average daily rate of 5.2 hours), while the G20 increased from 0.007 to 0.012 after 2,411 total hours (464 days).
This behavior was expected, and explained by Panasonic as a normal part of its plasma TVs' operation when we first documented it with 2009 models. The company previously said in a statement that its 2010 plasmas would incorporate a "more gradual change in black levels over time" than the 2009 models.
Response from Panasonic
This time around we were able to get much more specific information from Panasonic on the aging process. We spoke to Bill Schindler, a consultant and former vice president for the company, who told us that our 2010 review samples were operating within specification and, what's more, shouldn't change much more over the rest of their lifespans.
"Basically I was pleased to see your numbers are very much in line with what I received from the factory," Schindler told me. "You're basically at the end of the process on the G20. There will be one more tiny adjustment that will happen in the future, between 1,000 and 2,000 hours later, after which [MLL] will stabilize for the lifespan of the panel."
He characterized that adjustment as quite difficult to perceive and resulting in a change of, at most, 15 to 20 percent higher MLL--which, according to our math, would put the G20 at 0.014 ftl after the process is complete. He stressed that the numbers are approximate, however, and went on to say that the MLL might even improve slightly as the panel stabilizes.
Schindler didn't specify the exact stabilization point, but per his estimate we peg it at a maximum of 4,500 hours, which works out to 2.37 years. That time span jibes with what we were told by Panasonic Vice President Bob Perry in February: "...it would be safe to assume that around three years, more or less, is a reasonable approximation."
Perry was referring to the 2009 models at the time, but Schindler repeated today that the 2010 models have a much more gradual rate of MLL increase, meaning that the steps are finer and shouldn't result in any visible "jump" (and for what it's worth we didn't see any abrupt rise in MLL on any Panasonic plasma ourselves).
"Yes, it's more gradual this year," Schindler said, "and also doesn't go as far in terms of total span. Our engineers were able to become less aggressive with the voltage increase in 2010 and maintain the same reliability over time, which is their main objective."
As for the VT25, Schindler said it should follow the same curve of MLL increase as the G20. He expected that perhaps we would see one more small rise in MLL, after which it would stabilize. "At 1,500 hours you're on the cusp with that one, and it's impossible to tell whether you've already seen [the rise] or if it's about to happen."
According to our own estimates, based on the discussion with Schindler, we would expect that the "final" MLL for our VT25 sample would be 0.009-0.01 ftl at most. He was careful not to confirm or deny this estimate since, as he stressed several times, Panasonic (along with all other TV makers) does not specify black level.
Again, it's worth noting that these measurements are subject to error--we routinely saw variations of 0.001-0.002 ftl in our lab, so the numbers cited above are averages of several measurements. Accuracy depends on good instruments, a completely dark room and careful attention to content and picture settings.
The bottom line
Despite the near doubling of MLL on the VT25 and G20 we've measured so far, both still exhibit some of the best overall black level performance available on the market today. In order of "blackest" initial black, the other 2010 plasmas in our lab at press time include the Samsung PN50C7000 (0.017 MLL), Samsung PN50C8000 (0.019), and LG PX950 (0.030). All of these numbers are higher (worse) than our estimated "final" MLL of either Panasonic panel.
As a result we're not going to reduce the performance scores on the reviews of either 2010 Panasonic plasma TV at the moment. Both still deliver superb overall picture quality, and the VT25, even after the MLL increase, is still the best-performing TV of 2010 in our opinion. All of the comparisons in the Samsung PN50C8000 review, which includes most of the recent high-end TVs in our lab, were made after the VT25's MLL increase (see Performance for details).
Of course our evaluation might change if MLL increases in the future beyond what Panasonic has indicated, so we'll continue long-term testing of 2010 Panasonic plasmas through at least 4,500 hours. As do all TVs makers, Panasonic provided CNET with the samples for our evaluation--so panels in the field might not exhibit the same behavior.
It's also worth mentioning that we don't perform long-term tests on other brands of plasma or other kinds of televisions--we simply don't know, for example, whether the Samsung or LG plasmas also show MLL changes over time. At this point we have no plans to make long-term testing a systematic part of the process.
What's your take? Does this information influence your TV buying plans in general, or your opinion of Panasonic plasmas in particular? Should CNET devote resources to testing every TV we review long-term? Leave a comment.
Tests of Panasonic black level loss negative so far (8/19/2010)
Follow-up: Panasonic plasma black-level loss measured in long-term test (4/2/2010)
Tests point to extent of loss in Panasonic plasma black-level performance (3/2/2010)
Panasonic does not plan fix for reported black-level increases (2/9/2010)
Panasonic admits plasma TV black-level change but says picture quality still 'excellent' (2/4/2010)
Are Panasonic plasma TVs losing their dark black levels? (1/26/2010)