Understand key differences between Plasma and LED TV.

What is Plasma TV?

Plasma TV is a TV which uses Plasma Display Panel (PDP) for its screen. A brief history of how the PDPs came to be is given below before moving on to explaining the technology.

History

    • 1964: The first monochrome Plasma Display Panel was invented by the researchers at the University of Illinois.
    • 1980s: Research on multi color PDPs was going strong.
    • Late 1990s: First commercial color PDPs became available.
    • Now, PDPs with large screens and less thickness are easily available.

What is Plasma?

Plasma is a gas that consists of electrically charged particles- negatively charged free electrons and positively charged ions. In addition, Plasma also has uncharged particles called background gas. Rare gases like Neon and Xenon are used in Plasma.

Working of a Plasma Flat Panel Display

Plasma Display Panel consists of a grid of cells positioned between two parallel plates of glass with electrodes deposited on their surfaces. The electrode strips on the glass plates are actually perpendicular to each other forming the grid of cells. Individual cells are separated by barrier ribs. Inside walls of each cell is coated with red, blue or green phosphor. The tiny red, green and blue color elements together form a pixel. Each color cell can display 256 intensity levels, which means that each pixel can display over 16 million (256x256x256) colors. Schematic of a Plasma Display Pixel is shown below.

 plasma and ledThe gap between the two glass plates is filled with plasma. A voltage is applied across the electrodes which energize the particles in the plasma, thus causing a collision of free electrons with atoms. These collisions result in the atoms getting excited and their outer electrons jumping to a higher energy level. When these electrons fall back, they release energy as UV radiation. The UV radiation released by the plasma hits the phosphor material in the cell and gives off light in the visible region. The plasma used in PDPs is considered ‘cold’ plasma since the background gas does not get heated when voltage is applied.

Each individual cell can be turned on and off a number of times and with very high speed to produce a moving picture. They must be switched at a rate that creates 60 TV frames per second. Variation in light intensity is not done by changing the voltage applied. The effect is created by controlling the amount of time for which the pixel is on or off. Since eye response is much slower than the rapid switching rate, the eye perceives each color depending on how long the cell was on within the period of a TV frame. Plasma displays are a popular choice for HDTVs.

Benefits of Plasma TV

    • They are thinner than CRT.
    • They have flat screens and hence they free of distortion on the edge of the screen.
    • They display bright pictures of very good quality.
    • They have a wide viewing angle of 160 degrees.
    • It can track fast-moving images without motion blur. Therefore Plasma TV is ideal for watching sports or movies packed with action.

Plasma TV Drawbacks

    • The screen can experience a “color burn” if it is used excessively, i.e. when the television is turned off, a shadow of images may stay on the screen, and the color may be slightly faded in the areas that are burned. In spite of that, a plasma TV could last for over 60,000 hours of viewing time.
    • Plasma TVs use less electricity but have a slightly higher power draw than LED TVs.
    • These TVs are somewhat heavier.
    • They cost more to produce due to the use of noble gases.
    • They are expensive to repair and sometimes cannot be repaired at all.
    • Plasma TVs look better in low light than in bright light.
    • Plasma TVs are very fragile and need to be handled with care.

What are LED TVs

LED TVs are nothing but an improved version of LCD TVs. While LCD TVs use fluorescent tubes to light up the LCD screen which can be space consuming, heavy and inefficient in color quality, LED TVs use an array of LEDs to light up the LCD screen. Use of LEDs gives excellent picture quality where even purest blacks and whites are clearer.

Light Emitting Diode (LED)

LEDs are special kinds of diodes which emit light when electricity is passed through it. As mentioned earlier, when electron falls from higher energy level to lower energy level, a photon is emitted. In a diode, when electrons recombine with holes, photon is emitted. A silicon diode emits photon in the infrared region but there are other materials which emit photons in the visible region. These are called light emitting diodes and the light emitted depends on the material and the energy band gap between valence and conducting band.

Working of LED TVs

If Plasma display panels have plasma between two glass plates deposited with electrodes, in the case of Liquid crystal display (LCD) there is a layer of liquid crystals in between two conductive surfaces which act as electrodes. Liquid crystals are a state of matter that have properties between that of liquids and solids. ‘Liquid’ indicates that they can flow like liquids and ‘crystal’ indicates they form crystalline structures like solids. The alignment of the Liquid crystals controls how the LEDs’ backlighting is transmitted on to the screen and this alignment is controlled by applying an electric current to specific areas of the liquid crystal. Thus, the change in alignment along with LEDs’ backlighting generates on-screen imagery. LED TV screens avoid burn-in by using a technology called ‘twisting crystals’.

There are two types of LED TVs: Full-Array LED TVs and Edge-lit LED TVs.

    • Full-Array LED TVs
    • LEDs are placed at the back of the television panel.

Full Array LED TV Benefits

Back-lit LED TVs can selectively dim specific groups of LEDs, allowing for superior contrast ratio and superior overall picture quality. This feature is known as ‘local dimming’.

Drawbacks of Full Array LED TV

    • They are heavier than Edge-lit LED TVs.
    • They are costlier than Edge-lit LED TVs.

What are Edge-lit LED TVs

In these the LEDs are placed along the edge of the television sets. A light-diffusing panel spreads light from the outer edge of the set to the middle of the screen.

Benefits of Edge-lit LED TVs

    • They are thinner than back-lit LED TVs.
    • They are more power efficient.
    • The main advantage of edge-lit TVs over Full-Array TVs is the cost. Edge-lit TVs are relatively inexpensive.

Drawbacks Edge-lit LED TVs

    • The edge areas of the TV screen tend to be brighter than center of the screen. Sometimes "spotlighting" in the corners of the screen or "white blotches" scattered across the screen can be noticed, especially when dark scenes are viewed on TV. When viewing daylight scenes, these effects are not very pronounced. In recent times, a feature called ‘micro dimming’ has been introduced in edge-lit TVs to overcome this disadvantage, for example, Samsung’s UND8000 series. Sony uses the name Dynamic LED for the same technology.
    • Micro dimming varies the light output using light diffusers and light guides, which is less precise than local dimming used in Full-Array LED TVs.

Difference between Plasma and LED:

If you are to buy a TV and have to choose between Plasma and LED TV, these are the factors to be considered:

    • Plasma TVs are expensive. But Plasma TVs have been here for a while and the infrastructure required to manufacture Plasma TVs are now in place whereas LED TVs are still new. This makes LED TVs more expensive.
    • Plasma TVs are heavier than LED TVs, even Full-Array LED TVs.
    • Plasma TVs have a very wide viewing angle of 160 degrees. In the case of LED TVs, moving just over 75 degrees away from the center of the screen makes the images on TV look blur.
    • LED TVs perform well in bright as well as dark conditions. Even though Plasma TVs don’t perform well enough in bright light conditions, if you want a TV to watch movies in dark light conditions, for example home theatre, then Plasma TV is the one to go for.

 

Plasma

LED

Technology used in the TV screen

Plasma between glass plates

LCD screen: Liquid crystals between two conducting surfaces

Advantages

Thinner than CRT

Flat and free of distortion on the edge of the screen

Brighter than LCD

Energy efficient

Generates billions of colors

Long Lifetime

Environment friendly

Better picture quality

Lighter and thinner than LCD

Manufacturers

Panasonic

Fujitsu

Pioneer

Micromax

Sony

Samsung

Viewing Angle

160o

75o

Disadvantages

Fragile

Heavier

Difficult to repair

Adequate Heat-sinking required

Shift in color with age and temperature