Picture Degradation

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Could you paste a link to that? That's pretty interesting, I'd like to see how they measured the PQ there and what their conclusions were.


I'm guessing though that the DLP was due to the bulb dimming over time. I would think that if they had replaced the bulb after the test, the DLP would have been back to 0% degradation.


But if it degrades 22% in only 672 hours, that's going to get to be a lot of bulbs aftrer a while...

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The artucle makes use of the term "reflective microdevices" and "microdisplay" to describe the RPTV. The two technologies meeting this description are DLP and LCoS. Projection LCDs are transmissive microdisplays and projection CRTs are macrodisplays.


One of the problems with the test is that both LCD backlighting and the regulated electric arc lights used in the digital RPTV technologies experience rapid aging in early life, and calibration should not be performed until either has 500+ hours of use. Had this been done the reduction of brightness for the LCD and MCD displays would be a tiny fraction of the amount noted in the article.


The image retention results are bogus IMHO. If a plasma panel is subjected to several hours of usage with a high contrast pattern such as from a video game, the retained pattern would be noticeable for several hours during TV viewing immediately following the game usage. Such short duration dual use is typical of many households whereas the test methodology was clearly concocted to dispell permanent image retention myths.


The loss of brightness from plasma panels is also minimized by the brief 4-week duration of this test. I frequent an A/V store trhat occupies a mini-mall about 1/2 mile from my workplace, as it has several restuarants nearby. In late November they just turned over the floor model bigscreens including three brands of qualty high-dollar HD plasmas. When compared to a new panel, a 1-year old plasma that has been run 12 hours/day is notably faded. Furthermore those nearest the glass windows in front of the store were damaged the most, having had the 12 hours/day by 12 months at brightness and contrast settings higher than the panels in the darker areas of the store, where track lighting was strategicly placed to reduce ambient light levels.


I'll have to say that overall my opinions are not swayed by this document.


Gary

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Gary, can you please elaborate on what you've seen in terms of loss of brightness?


Running the plasmas 12 hours a day for a year would only be about 4380 hours of use, or 7% of the expected half-life of most plasmas (60k hours). It may be understandable that having the settings with the brightness and contrast cranked up would have an effect, but 1 year seems to be pretty short.


I'm also surprised by the degree of degradation of the PDP from the white paper. With only 672 hours of use (a little more than 1% of the expected half-life) there is already 5% degradation in brightness? Using this as a guideline, would a reasonable conclusion be that you would hit the half-life point in less than 7000 hours?

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Not really...


What you have to understand is that the decay rate in phosphor brightness is NOT a linear function... rather, it is closer to an inverse exponential function.


Assuming the decay of brightness was a true inverse exponentional function, we would expect after 672 hours of usage the brightness would be about 98% of the original (also assuming a half-life of 40,000 hours)-- this is a 2% loss.


However, we know that phosphor brightness decay starts out fast and then slows down, so it is not too surprising to see the loss in this sort of test come out at 5%.


It's also not suprising to see LCD and RPTV brightness down so much either for the same reason-- in a sense, it is kind of unfair as their initial decay rates are greater (but long-term decay rates overall are fairly similiar) and that is really the only thing this test demonstrates.

I think the missing factor in the tests is the settings for contrast and brightness. The PDP's I have observed with visibly degraded outputs were those that were located in the front of the store I mentioned near the South-facing wall of glass windows. All day long they were running in "torch mode" with very high brightness and contrast settings, for a 12-month period. They were bright enough to look good in conditions of sunlight and California clear skies.


YES they were abused - but my point is that a PDP so adjusted for usage in very bright room would have a much shorter half life than 60,000 hours. I am interested because I am seeking a new 32-42" HDTV for such a South-facing room with a cathedral ceiling and a side wall with a large half-circular window, for which I have been unable to locate a form of room-darkening window treatment the wife will accept. I think the high daytime ambient light precludes a PDP or a RPTV of any type, and I want to be able to view in daylight or dark lighting. An LCD panel display with adjustable backlighting would appear to be my best option.


Gary