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Plasmas and CRTs have phosphors -- materials that react when "excited" by electrons of sufficient energy. These phosphors then glow and you see pretty colors (and pictures). The problem is that the very process of "exciting" the phosphor also uses it up ever so slightly. Over a period of time, the phosphor literally breaks down and so your screen gets dimmer and dimmer.


Now, this breakdown is more logarithmic so its actually always slowing down. As a result, your TV will get more dim in its first 1000 hours (as measured by how much light it puts out) then it will between hours 7000-8000. Current plasmas are generally assumed to lose half their brightness in about 20,000 hours of use.


LCDs, by contrast, generate all their light without phosphor excitation. Instead, they have fluorescent lamps sitting behind the panel. Fluorescent lamps can go for 30,000-60,000 hours and can even be replaced in some designed. While they become somewhat less bright over time, it's not so much.


In the meantime. the individual pixels in an LCD are controlled by transistors that cause a crystalline material (which is liquid) to twist or not in such a way to allow light to pass through or not. The transistors are effectively switches that last nearly forever. The crystal material generally returns to its original normal state after being switched off and also lasts nearly forever.


So in an LCD, no invidual pixel can retain an image. Either the whole panel works or it doesn't. In a plasma, an individual pixel might be "used up" more or less than a neighboring pixel. What everyone describes as "burn in" is a bit of a misnomer. It's not that something is burned in and you always see it, it's that those pixels are less bright than their neighbors, so you get an after-image of whatever used up those pixels.


Make sense?


Mark
 

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 http://www.presentationmaster.com/20...res/plasma.htm


I dug up this article from 7 months ago comparing these "apples to oranges". It discusses why plasmas burn in and a host of other differences. Why plasmas have a faster response time but use more energy than LCD. And why they have more even color uniformity than LCD. Some interesting statements made by the folks being interviewed ie "LCD takes the honors for having the blackest blacks..." which may contradict posts I've seen on this forum. It also suggests that LCDs should be cheaper to make.


I think both these technologies will continue to have advantages and disadvantages over each other. And that the competition will continue to benefit consumers - both in PQ and price.


-- Jeff
 

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Jeff: Good link. I am curious if anyone can find an example of black level being measured lower on the best LCDs than on the best plasmas. I don't believe Pete Putman's reviews have done that but I'm not familiar with other reviewers who measure black level.


In Putman's most recent review, the Sharp LCD tests out as the blackest black at 0.7 nits. The best plasma blacks are 0.2 nits, from Panasonic and Fujitsu -- a much lower black level. And many plasmas beat the Sharp's spec. So it's kinda hard to believe LCDs have intrinsically better blacks.


Mark
 

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Refresh is better on the newest LCDs targeted at the video market.
 

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Quote:
Originally posted by wiscy
http://www.presentationmaster.com/20...res/plasma.htm

(...) Some interesting statements made by the folks being interviewed ie "LCD takes the honors for having the blackest blacks..." which may contradict posts I've seen on this forum. (...)

-- Jeff
Jeff,


I think these people either don't understand what they're talking about...

Rendition of blacks is only a subset of the real issue which is gray-scale reproduction.


Blacks can be achieved quite easily by blasting the viewer with a high-brightness display. This closes irises in the viewer's eyes, which "turns" dark grays into "blacks." Of course, this trick falls apart when viewing dark scenes without any bright objects in them...


The 3 desirable characteristics of any display are: wide gray-scale dynamic range (contrast ratio), smooth gray-scale reproduction, and accurate color.


Problems with limited gray-scale range can be clearly seen on Sony's GWII LCD-based TV when compared to CRT-based TVs side by side (visit your local Circuit City).


Mike
 
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