| Video Noise September 2003
So You Want Plasma?
In recent years, older display technologies have been
improved to such a degree that they are now in a completely different league. Pick a price
from $800 and up, and today’s video displays will clean the clock of any display made
five years ago. But new display technologies, each claimed to be "the next big
thing," continue to challenge the old-guard technologies. Each new technology has its
share of visible problems, some of which you can’t get rid of no matter how much
money you throw at them. Getting artifact-free high-definition performance down to
real-world price levels continues to elude display manufacturers -- but they’ll get
there, given time and steady progress. Many people have gotten interested in plasma
displays from aggressive television and magazine advertising. Product placements on
popular TV shows, especially the hip shows watched by twenty-to-thirtysomethings, have
also helped raise the profile of plasma screens, and people’s desire to own them.
Plasma screens have captured people's interest because
they’re so thin. They can be hung on a wall or set on top of a shelf or table. Their
shape alone has made them something of a pop hit -- even if they’re still too
expensive to be in the homes of everyone who wants one. Today’s plasmas are most
often 16:9 widescreen models in the 42" to 63" range. But plasma screens are as
small as 32" and as large as 84", at prices ranging from $2500 to $25,000 and
up.
Plasma screens rely on phosphors similar to those in
conventional picture tubes. The phosphors in a conventional TV tube glow from being
excited by an electron beam projected onto them. Plasma-screen phosphors are inside tubes
that are almost microscopically small. An electronic switching network applies power to
the tubes, generating plasma within the tubes. The plasma causes the phosphor coating
inside the tube to glow.
Here is a summary of some of the pros and cons concerning
plasma video displays, to help you decide if one is for you.
Plasma pros
After decades of conventional picture tubes’ flawed
geometry, plasma screens offer perfectly straight lines and perfectly round circles. You
won’t get color fringing, because there are no electron beams to be misaligned. On a
good plasma display in a room with little or no light, bright, colorful images look
absolutely stunning.
The prices of plasma displays are a little lower each year.
I’ve seen the prices of some plasmas drop as much as 30% in 12 months, but that
won’t happen every year -- you’re more likely to see prices drop 5% to 10% per
year for sets of similar size and features. And as prices drop, image quality tends to
improve -- that’s not what you might expect, but for plasma screens, it’s
usually true.
Unlike many other large-screen display technologies,
plasmas look great when you’re sitting way off to the side. It doesn’t matter if
you sit, stand, or lie on the floor -- a plasma image will look good from any reasonable
angle. And if you don’t have high expectations of great video quality, you can watch
a plasma in a daylit room.
Plasma cons
To avoid being disappointed by a new technology, it’s
best that the potential buyer know what its weaknesses are. If those weaknesses limit the
technology’s appeal, perhaps you should look for something else.
Even the most expensive plasma screens -- those costing
$20,000 and up -- can’t produce blacks that are any darker than charcoal gray. Most
people don’t understand what that means until they view a scene that includes
fireworks, or such movies as Daredevil or Batman, in which blacks and
shadows make up significant areas of the image. Compare the appearance of the fireworks or
dark scenes on the plasma to a properly set-up CRT display: On the plasma, the dark scenes
look flat and lack detail, with only gray in areas of the image that should be black --
and would be black on a properly adjusted display, a conventional CRT TV, or a
rear-projection TV.
Budget plasma screens have low prices for a reason: they
have fewer pixels than more expensive plasmas. Fewer pixels means lower resolution. The
lowest-priced plasma displays sometimes have little more resolution than a conventional
"old tech" TV that can’t display HDTV. Smaller plasma screens also tend to
have fewer pixels. This means that if you see a 60" plasma screen with 1400x1100
pixels, the 42" version of the same brand may have 1000x700 pixels. You can make
plasma pixels only so small before you have to start giving up pixels to get a smaller
screen size. Only the largest plasma displays are beginning to approach the number of
pixels needed to display every pixel in an HDTV image. This means that when you watch HDTV
on most plasmas, you’re seeing lower-than-HDTV resolution. The images still look
good, but not as good as they would with every HDTV pixel present and displayed.
Plasma screens have not yet reached their peak image
quality, which continues to improve every year in just about every model. Some years, the
improvements are easy to see; in others, the improvements are subtle. But the technology
continues to improve. This is a pro and a con -- while this year’s plasma
screens are the best ever, next year’s might be much better.
Plasma screens are "fixed-pixel" displays. Every
video source -- conventional TV, DVD, HDTV, etc. -- has a different resolution. Some
plasmas have a resolution that matches no standard video format; every image you
see on such screens must be up- or downconverted to the actual resolution of the screen,
called the "native" resolution. Electronics that convert one video format to
another are difficult to design well. As you might expect, the lower a plasma’s
price, the cheaper its format-conversion technology, and the more noticeably its image
quality will suffer. The quality of format conversion is one of the more important ways in
which plasma screens can differ.
There are hidden "plasma taxes." Buyers are
frequently unaware that the prices posted on some plasma displays get you a set that
won’t do anything. You often have to buy an extra box or circuit board, which might
raise the cost of the display by $200, for minimal functionality, or by $1500 or more, for
better conversion boards that will let you connect the same equipment and view the same
programming as many $2000 rear-projection high-definition displays. When researching your
purchase, make sure you understand what extras you’ll have to buy to make the plasma
do what you want it to do. One display I looked at recently sounded like a good deal, but
in order to do the things you’d expect any modern video display to do, it needed a
circuit board that allowed it to display high-definition video, display picture-in-picture
(PIP), and receive analog cable channels and conventional analog broadcast signals. The
board added $1000 to the price. Suddenly, that plasma didn’t look like such a good
deal.
Some plasma screens include no feet or mounting bracket of
any kind -- if you want feet or a bracket, you pay extra for them.
Plasma screens will wear out over time. I’m not sure
anyone really knows how long a plasma will last, or whether or not it will "die"
faster than a conventional CRT tube. One thing is certain: the brighter the picture it
displays, the faster the phosphors will age. There are confirmed reports of network logos
being burned into plasma screens. This tends to happen when a set is used during the day
in a brightly lit room. Crank up the Picture control to see what’s happening on the
Disney channel in a bright room and leave it at that setting, and Disney’s logo will
soon be visible on every image you display.
Plasmas aren’t perfect. When your new display is
delivered, it could have one or more dead pixels. A dead pixel is most likely to appear as
a colored speck darker than the area around it, and most easily seen when an area of the
screen is all one bright color, or white. A single dead pixel is not terribly noticeable;
but as the set ages, more pixels may die.
As you can see, plasma displays have more cons than pros.
Still, plasmas are interesting products that may be perfect for some people. Knowing the
strengths and limitations of this emerging technology helps set realistic expectations
that will assist you in making better buying decisions.
...Doug Blackburn
db@hometheatersound.com |
