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Follow-up: Panasonic plasma black-level loss measured in long-term test

CNET's long-term test of two in-house Panasonic plasmas has revealed a black-level rise, impairing picture quality somewhat, after a certain number of hours of use.

This 2009 Panasonic V10 plasma in CNET's lab now produces a black about as deep as that on a Samsung. CNET/Sarah Tew

Previous CNET tests of Panasonic plasma TVs measured differences in black-level performance seemingly related to the age of the televisions. New results from our follow-up testing further confirms that relationship.

On January 26, after we heard about the potential problem, we began long-term tests of two 2009 Panasonic plasma review samples we had in our lab, a TC-P50V10 and a TC-P54S1. Now, after about 1,000 hours of use, each TV has shown an increase in the level of "black" it can produce, leading to decreased overall picture quality.

The latest measurements of the V10 reveal a black level of 0.016 footlamberts at 982 hours of use, compared with the 0.008 we measured previously. Black on the S1 measures 0.017 after 1,012 hours, compared with a previous 0.011.

These results are similar to increases we measured on a TC-P50G10 and a TC-P42G10. Neither was aged under controlled conditions in our lab, but both reproduced black at 0.023 ftl after about 1,500 hours (at the average rate of 5.2 hours per day, a TV logs about 1,900 hours in a typical year). We suspect that more aging of our two in-house models will result in similar rates of increase, but only further testing will tell.

In comparison, the deepest black levels we've recorded are 0.001 ftl--as low as our Konica Minolta LS-100 meter will accurately measure--seen on models like the LG LH8500, the Samsung UNB8500, and the Pioneer Kuro. Samsung's 2009 PN50B650, a direct competitor to Panasonic, measured 0.018. We do not have hours of use data for non-Panasonic TVs in our lab, but we have no evidence that other TVs, plasma or otherwise, show similar losses in black-level performance over such periods of time.

Panasonic has indicated that it has modified its 2010 line of plasma TVs to introduce a "more gradual change in black level over time." We have yet to test any 2010 Panasonic plasma--the company promises to deliver a review sample in the next couple of weeks--but when we do we will also conduct long-terms tests as best we can. We are also exploring a long-term test regimen for other TV products, but can't promise anything yet.

See below for more information, in-depth discussions, and buying advice on this issue.

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)