Plasma displays, their advantages and disadvantages. Which is better: Plasma or LCD TV

What is Plasma?

The basis of every plasma panel is the plasma itself, that is, a gas consisting of ions (electrically charged atoms) and electrons (negatively charged particles). Under normal conditions, a gas consists of electrically neutral, i.e., no charge particles.

Individual gas atoms contain an equal number of protons (particles with a positive charge in the nucleus of an atom) and electrons. The electrons `cancel out 'the protons, so that the total charge of the atom is zero. If you introduce a large number of free electrons into a gas by passing an electric current through it, the situation changes radically. Free electrons collide with atoms, knocking out more and more electrons. Without an electron, the balance changes, the atom acquires a positive charge and turns into an ion. When an electric current passes through the resulting plasma, negative and positively charged particles tend to each other. In the midst of all this chaos, particles are constantly colliding.

The collisions 'excite' the gas atoms in the plasma, causing them to release energy in the form of photons. Plasma displays mainly use inert gases - neon and xenon. When excited, they emit light in the ultraviolet range invisible to the human eye. However, ultraviolet light can also be used to release photons in the visible spectrum.

The history of the creation of plasma panels or screens

Everything was for the defense industry. Even if the scientists themselves thought they were working for their own pleasure. They were wrong.

It was 1963. Donald Bitzer of the University of Illinois has worked on learning systems to display not only letters and numbers, as was the case at the time, but also graphics. Success in this field was poor.

Eventually Bitzer recruited a team to work on a new project. He was going to figure out how a matrix of neon cells would work if a high-frequency electric current was passed through them.

For his work, Bitzer recruited Zhene Slottov and student Robert Wilson. It is no longer clear how things were going, only all three names are inscribed in the patent for the invention.

In the summer of 1964, the first plasma display appeared. It looked very remotely like modern panels. Funny, but it consisted of only one single pixel. Now there are millions of them in each panel.

Naturally, a single pixel display is not a display. However, less than ten years later, acceptable results were achieved. In 1971, Owens-Illinois was licensed to manufacture Digivue displays.

In 1983, the University of Illinois earned no less than a million dollars for the sale of the plasma license to IBM. Now she began to gradually recede into the shadows, and then there was no stronger player in the computer market at all.

Plasma displays were first used in PLATO computer terminals. This PLATO V model illustrates the display with the monochromatic orange glow seen in 1981.

In the same year, the IBM 3290 Information Panel, the first commercial product to be released in mass circulation, appeared.

Already in 1982, they began to produce Plasmascope displays for monitoring the launches of ground-based ballistic missiles. True, at that time it did not help them very much. In general, computer firms quickly abandoned plasma displays. IBM was the last to abandon their production in 1987. By that time, only the Pentagon was producing plasma in limited quantities. He always had plenty of money.

By the early nineties, commercial LCDs were on the way, and plasma was not doing well. Then only black-and-white plasma panels were produced and they, in general, could not compete with LCD. And the problems with contrast did not please - this indicator was lame even in the most advanced models. Nonetheless, Plasma has taken root in Matsushita, now known as Panasonic. In 1999, a promising 60-inch prototype was finally created with outstanding brightness and contrast, the best in the industry.

In the late 90s. Last century Fujitsu managed to alleviate the problem by improving the contrast of its panels from 70: 1 to 400: 1. By 2000, some manufacturers declared contrast ratios of up to 3000: 1 in panel specifications, now it is already 10000: 1+. The manufacturing process for plasma displays is somewhat simpler than the manufacturing process for LCDs. In comparison with the release of TFT LCD displays, which require the use of photolithography and high-temperature technologies in sterile clean rooms, `plasma` can be produced in dirtier workshops, at lower temperatures, using direct printing.

Plasma technology

Based on the information in the video signal, a powerful electron beam “ignites” thousands of small dots called pixels. Most systems have only three pixel colors - red, green, and blue - that are evenly distributed across the entire screen. By mixing these colors in various proportions, televisions can reproduce the full range of colors.

Plasma display is created by glowing small colored fluorescent bulbs. Each pixel is made of three fluorescent bulbs - red, green and blue. Due to the different brightness of the bulbs, like CRT TVs, plasma panels can reproduce the entire color gamut.

The centerpiece of fluorescent light bulbs is plasma, a gas made up of free ions (charged atoms) and electrons (negatively charged particles). Under normal conditions, a gas consists of uncharged particles, that is, atoms with an equal number of protons (positively charged particles located in the nucleus of an atom) and electrons. Negatively charged electrons neutralize positively charged protons, as a result of which the total charge of an atom is zero.

If you add a large number of free electrons to a gas by passing an electrical discharge through it, the situation will change very quickly. Free electrons colliding with atoms<выбивают> of which valence electrons. With the loss of an electron, the atom acquires a positive charge and thus becomes an ion.

When an electric current is passed through the plasma, negatively charged particles are attracted to the positively charged region of the plasma, and vice versa.

Moving rapidly, the particles constantly collide with each other. These collisions excite the gas atoms in the plasma, and they emit photons.

The xenon and neon atoms used in plasma panels emit photons of light when excited. These are mainly ultraviolet photons that are not visible to the naked eye, but, as we will see in the next paragraph, they can activate visible photons of light.

Inside the panel: gas and electrodes

Plasma displays contain xenon and neon in hundreds of small microchambers located between two glass panes. On both sides, between glasses and microchambers, there are two long electrodes. The control electrodes are located under the microchambers along the rear glass. Transparent scanning electrodes, surrounded by a dielectric layer and covered with a protective layer of magnesium oxide, are located above the microchambers along the front glass.

The electrodes are positioned crosswise across the entire width of the screen. The scanning electrodes are located horizontally and the control electrodes are located vertically. As you can see in the diagram below, the vertical and horizontal electrodes form a rectangular grid.

To ionize the gas in a specific microchamber, the processor charges electrodes directly at the intersection with this microchamber. Thousands of such processes take place in a split second, charging each microchamber in turn.

When the crossing electrodes are charged (one negatively and the other positively), an electrical discharge passes through the gas in the microchamber. As mentioned earlier, this discharge sets charged particles in motion, as a result of which the gas atoms emit ultraviolet photons.

Plasma screen

Plasma displays are a bit like CRT televisions - the display coating uses a phosphorus compound that can glow. At the same time, like LCDs, they use a grid of electrodes with a protective coating of magnesium oxide to transmit a signal to each pixel-cell. The cells are filled with internal gases - a mixture of neon, xenon, argon. Electric current passing through the gas makes it glow.

Basically, a plasma panel is an array of tiny fluorescent lamps controlled by the panel's built-in computer. Each pixel-cell is a kind of capacitor with electrodes. An electric discharge ionizes gases, converting them into plasma - that is, an electrically neutral, highly ionized substance, consisting of electrons, ions and neutral particles.

Electrically neutral, plasma contains an equal number of electrons and ions and is a good current conductor. After discharge, the plasma emits ultraviolet radiation, causing the phosphor coating of the pixel cells to glow. The red, green or blue component of the coating. In fact, each pixel is divided into three subpixels containing red, green, or blue phosphorus. Each sub-pixel is independently controlled to create a wide variety of color tones. In CRT TVs this is done by changing the intensity of the flow of electrons, in `plasma '- using 8-bit pulse code modulation. The total number of color combinations in this case reaches 16,777,216 shades.

The fact that plasma panels are themselves a light source provides excellent vertical and horizontal viewing angles and excellent color reproduction (unlike, for example, LCD screens, which usually require matrix backlighting).

Inside the display

In a plasma television, neon and xenon gas bubbles are placed in hundreds and hundreds of thousands of small cells, squeezed between two glass panels. Long electrodes are also located between the panels on both sides of the cells. The 'addressable' electrodes are located behind the cells, along the rear glass panel. The transparent electrodes are coated with a dielectric and a protective film of magnesium oxide (MgO). They are located above the cells along the front glass panel.

Both electrode grids cover the entire display. Display electrodes are arranged in horizontal rows along the screen, and addressable electrodes are arranged in vertical columns. As seen in the figure below, the vertical and horizontal electrodes form a baseline grid. In order to ionize the gas in a separate cell, the plasma display computer charges those electrodes that intersect on it. It does this thousands of times in a fraction of a second, charging each display cell in turn. When the crossing electrodes are charged, an electrical discharge is passed through the cell. The flow of charged particles causes the gas atoms to release photons of light in the ultraviolet range. The photons interact with the phosphoric coating of the inner wall of the cell. As you know, phosphorus is a material that, under the influence of light, emits light itself. When a photon of light interacts with a phosphorus atom in a cell, one of the electrons of the atom is transferred to a higher energy level. The electron then shifts backward, releasing a photon of visible light.

The pixels in a plasma display panel are made up of three sub-pixel cells, each with a different coating of red, green or blue phosphor. In the course of the panel operation, these colors are combined by the computer, new pixel colors are created. By changing the rhythm of the pulsation of the current passing through the cells, the control system can increase or decrease the intensity of the luminescence of each subpixel, creating hundreds and hundreds of different combinations of red, green and blue colors. The main advantage of plasma display manufacturing is the ability to create thin panels with wide screens. Because the luminosity of each pixel is individually determined, the image comes out stunningly bright, and when viewed from any angle. Normally, the saturation and contrast of the image is somewhat inferior to the best models of CRT TVs, but it fully meets the expectations of most buyers. The main disadvantage of plasma panels is their price. It is impossible to buy a new plasma panel cheaper than a couple of thousand dollars; hi-end models will cost tens of thousands of dollars. However, over time, the technology has improved significantly, prices continue to fall. Now plasma panels are beginning to confidently crowd out CRT TVs. this is especially noticeable in rich, technologically advanced countries. In the near future, "plasma" will come to the homes of even poor buyers.

Service life of plasma panels

The lifespan of plasma panels is measured relative to the phosphorus gas half-life. According to the manufacturers, after all the phosphorus has burned out, the image quality is significantly degraded from the original, and the panel may need to be replaced. In this case, the half-life of the combustion is exactly half the life of the panel.

After 1000 hours of operation, the brightness level is approximately 94% of the original.

Since phosphorus is burned at a constant rate, image quality deteriorates in proportion to the rate of decay. You can think of this process as simply "glowing" phosphorus. Immediately after turning on the plasma television, the phosphorus contained in the screen starts to burn slowly. Thus, there is less and less gas for the screen to glow. As a result, the brightness and color saturation gradually decrease. After 1000 hours of operation, the brightness level is approximately 94% of the original; after 15000-20000 - about 68% (i.e. 68% of phosphorus glows). Much depends on the level of contrast. If you want the plasma panel to last longer, lower the contrast in the OSD. If you set the contrast ratio to maximum, phosphorus will burn much faster.

Most manufacturers claim that their panels will last approximately 30,000 hours at "normal" contrast levels (around 50%). Recently, however, some manufacturing companies, notably Sony and Panasonic, have stated that the picture quality of their new plasma TVs begins to decline after 60,000 hours of use. We are a little skeptical about such claims. Although we realize how much has been done to increase the service life of plasma TVs (for example, the increased stability of green phosphorus), we will still believe these data only after they are confirmed in real conditions, and not only theoretically.

From a shopper's point of view, 30,000 hours should be sufficient as the lifespan of CRT TVs is roughly the same. On the other hand, according to a study by American statistical companies, an average family watches TV from 4 to 6 hours a day; accordingly, the service life of the plasma panel will be from 13 to 20 years.

How to Extend Panel Life?

Follow these guidelines to extend the life of your Plasma TV:

• 1) Adjust the BRIGHTNESS and CONTRAST level according to the viewing conditions. Try not to increase the Contrast level unnecessarily - this will only burn phosphorus faster. In brightly lit rooms, you may need a higher Contrast; at night or in dark rooms, the Contrast level should be reduced. *
• 2) Do not leave a static image on the screen for long periods of time (more than 20 minutes). Otherwise, an afterimage will appear on the screen.
• 3) Turn off the plasma display after viewing.
• 4) Use the plasma TV in a well-ventilated area. Thanks to a high-quality ventilation system, the plasma screen will last longer.

* Recently, most manufacturers "take out" the option of adjusting the contrast on the remote control; you do not need to enter the on-screen menu.

How to avoid burning out the plasma panel?

In addition to the question of the lifespan of plasma TVs, buyers are often interested in screen burn-in, which manufacturers claim is the result of improper use of the panel. This is all very serious; Accordingly, the question arises: What is the burnout of plasma panels, and how should they be used to avoid such an effect?

Burnout is most commonly seen on ATM screens. We are all familiar with the result that the same picture - the "insert card" section of the menu - is displayed on the screen for too long. Have you noticed how this gray inscription looms in the background during the entire operation with the ATM? This is the screen burn-in effect; it is permanent.

Without going into technical details, burn-in is a damaged pixel, whose phosphorus has been used up prematurely and, therefore, it glows fainter than the surrounding pixels. The reason lies in the fact that the damaged pixel "remembers" the color with which it glowed for a long time. This color is “burned out” on the glass of the plasma screen (hence the term “burnout” originates). Damaged phosphorus cannot glow like normal phosphorus.

Pixels usually do not burn out one by one, as this effect appears due to prolonged display of a static picture on a plasma screen - for example, network logos, computer icons, Internet browser windows, etc.

Tips

• 
  Do not leave a static image on the panel screen. Always turn off the panel after viewing. Do not pause DVD for long periods of time.
• Plasma screens are more likely to burn out within the first 200 hours of use. "Fresh" phosphorus burns faster than used phosphorus. This means that new plasma displays are more likely to experience a “halo” appearance after prolonged projection of a static image. This is probably due to the fact that due to the high brightness, "fresh" phosphorus explodes. Usually, this effect disappears by itself after a while. If you leave a static image on the screen for a long time, screen burn-in may follow the halo effect.

Precautionary measures: Be careful when turning on the panel for the first time. Set the CONTRAST level to no more than 50% - exceeding it will lead to more intensive combustion of phosphorus and, as a result, burnout of the screen. Use the anti-burn features provided, such as the grayscale function, which removes ghosting by recalibrating pixel brightness. Ideally, this feature should be used approximately every 100 hours of plasma display. (Note: These processes affect the phosphorus resource, so they should only be used when necessary.)

Some plasma displays burn out more often than others. It has been observed that users of AliS panels - manufactured by Hitachi and Fujistu - are more likely to experience screen burn-in.
Use anti-burn features such as power management, picture control (vertical and horizontal) and automatic screen saver. Check your user manual for more information.

It is important to understand that image quality is directly related to screen burn-in. You are looking to purchase a plasma TV for watching TV programs in 4: 3 format. Do not leave black streaks on the plasma TV screen for a long time; therefore, TV programs are best viewed in widescreen mode (16: 9). With good scaling, you will not notice a significant difference in image quality.

High-quality TVs are more resistant to burn-in, although not completely. Of all the plasma panels that had to be tested, the models from NEC, Sony, Pioneer and Panasonic were the least susceptible to burnout. Despite this, experts NEVER, regardless of the quality of the panel, leave a static image on the screen for more than an hour.

You should understand that some applications are not suitable for use with plasma displays.

For example, a static display of the airport flight schedule. One can often be surprised when entering an airport by a completely burnt-out plasma monitor hanging from the ceiling. The only thing they are used for is projecting the same information for hours. This is one of the many examples where plasma displays are being misused. (Note that recently airports have started using new software that constantly moves the image to avoid burning out the plasma monitor.)

conclusions

The burn-in effect is not a reason not to buy plasma TVs. When used properly, most plasma panel users will never experience image retention. A halo effect can sometimes occur, but this is not a cause for concern. In fact, carelessness - that is, indifference to what a plasma panel displays for how long - is the main cause of screen burn-in.

The MTechnic service center carries out prevention, diagnostics and repair of LCD TVs, repair of projection TVs and repair of plasma panels of the following brands: Sony (Sony), Thomson (Thomson), Toshiba (Toshiba), Panasonic (Panasonic), LG (LG) , Philips (Philips), Grundig (Grundik), Samsung (Samsung), RFT (RFT) and other manufacturers.

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