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.
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