Plasma Televisions - Big Television Sets You Can Hang on Your Wall
Since their US debut in 1999, plasma televisions
have significantly changed the television set market. After all, who wouldn't want
a television you can hang on the wall?
Plasma television technology even has a science-fiction like name that
sounds as if it's been taken from Star Trek or maybe Ghostbusters.
When you visit an electronics store's TV display floor and want to be left
alone, just ask any approaching sales person what is the plasma
in plasma televisions. In the rare occasion this technique backfires
and you actually do get a long explanation, you're on your own, though!
In reality, plasma televisions are no more "science fictional" than fluorescent
lights. Each light dot in a plasma television screen is like a little fluorescent
lamp, containing a gas plasma cell, a pair of voltage inducing electrodes,
and light emitting phosphate material.
Plasma is a state of matter like gas, but in which the atoms are ionized,
that is, some of the electrons have left the atoms and are free floating. Plasma
can be formed using high voltage. In fluorescent lamps, plasma is used to create
ultraviolet radiation that hits the phosphorous coating of the lamp, which them
emits light photons. (That's the short, short version.)
Basic plasma screen technology was invented in 1964 at the University of Illinois.
Monochrome plasma screens were first used for laptop computers in the late 80s,
and due to the large cost of making large plasma screens,
it wasn't until the late 90s that plasma televisions appeared on the market.
Benefits of Plasma Television Display Technology
Plasma television technology enables televisions to be made thin (3-4 inches)
compared with the old CRT technology. Consequently, they
take much less space out of the living room, and can also be mounted on the wall
like a picture.
Plasma televisions enjoy a wide 170 degree viewing field.
(180 degrees is the maximum possible.) Other flat screen technologies,
in particular, rear projection and LCD, suffer from a narrow field of view, i.e.
when viewed a bit off center, the picture becomes very difficult to see.
Plasma television sets are not susceptible to magnetic fields. Magnetic fields
pose a problem to the standard cathode ray tube (CRT) based televisions. CRTs
rely on an electron beam to create their picture, and electron beams can be
misdirected by magnetic fields. Worse yet, strong magnetic fields can permanently
magnetize components of the CRT screen, creating discolorations and uneven spots.
To make things even worse for CRTs, home theater components, especially speakers,
contain strong magnets. For plasma televisions, proximity to strong magnets
is not a problem.
Plasma display technology produces pictures that are bright (not as bright as
LCD televisions though), sharp,
uniform (no dark spots), and can display a large amount of colors.
Disadvantages of Plasma Televisions
Since plasma television emit light using phosphorous materials,
they are susceptible to screen burn-in.
Screen burn-in happens when static screen images illuminate
the same sections of phosphor for long periods of time, thus darkening the phosphor
material and resulting in faint ghost images of what was displayed in the past.
Static images with high contrast are particularly problematic.
High contrast images have dark areas next to bright ones right next to each other.
So, white letters on black background, for example are likely to cause burn in.
But, yellow letters on a blue backgound are just as bad because a yellow pixel contains
the blue and green of an RGB triplate, and a blue pixel contains just blue, therefore
resulting in high contrast in green.
The burn in problem was ubiquitous in CRT computer screens, leading to the advent of "screen savers".
Plasma screens may be in danger of burn-in after about 15 minutes of showing the
same picture. Many plasma televisions contain built in screen saving features, such as
automatically moving the image by a couple of pixels every few minutes, or
automatically reducing image contrast.
Plasma televisions tend to lose their brightness over time.
A typical plasma television will lose half its brightness after about 25,000
hours of operation. This number varies by model. There is no fix for
this problem, and once it's noticable you'll just have to buy a new TV.
But the good news is that 25,000 hours will give you many years of normal
nousehold use, and you'll probably want to get a new television
for other reasons before it becomes a problem.
Plasma televisions are not a good match with high altitude operations.
The low air pressure in high altitudes causes the relative pressure of the plasma
gas to go up, increasing the stress on the plasma screen.
This effect increases the power needed to run and cool the television,
making cooling fan noises more noticable. Plasma displays typically
start having trouble at about 6000 feet, but check the manufacturer's instructions
for specific high altitude opperations recommendations for your TV.