Mumbai university > Electronics and telecommunication Engineering > Sem 6 > Television Engineering

Marks: 05

Years: Dec 2016

Plasma:

• Plasma television technology is based loosely on the fluorescent light bulb. The display itself consists of cells.

• Within each cell two glass panels are separated by a narrow gap, in that includes an insulating layer, address electrode and display electrode, in which neon-xenon gas is injected and sealed in plasma form during the manufacturing process.

• When a Plasma TV is in use, the gas is electrically charged at specific intervals.

• The charged gas then strikes red, green and blue phosphors, thus creating an image on the Plasma TV screen.

• Each group of red, green, and blue phosphors is called a pixel (picture element - the individual red, green, and blue phosphors are referred to as sub-pixels).

• Due to the way that Plasma technology works, it can be made very thin.

• However, even though need for the bulky picture tube and electron beam scanning of those older CRT TV is no longer required, Plasma TVs still employ the burning of phosphors to generate an image.

• Thus, Plasma TVs still suffer from some of the drawbacks of traditional CRT TVs such as heat generation and possible screen-burn of static images.

LED:

• LED stands for light-emitting diodes which are exactly what a LED TV uses to illuminate the images displayed on the screen.

• On a LED screen, however, the light-emitting diodes can be placed either behind the screen or around its edges.

• LED TVs provide a better picture for two basic reasons. First, LED TVs work with a colour wheel or distinct RGB-coloured lights (red, green and blue) to produce more realistic and sharper colours.

• Second, light emitting diodes can be dimmed. The dimming capability on the back lighting in a LED TV allows the picture to display with a truer black by darkening the lights and blocking more light from passing through the panel.

• This capability is not present on edge-lit LED TVs; however, edge-lit LED TVs can display a truer white than the fluorescent LED TVs.

• With Edge Lighting, LED TVs produce light from a series of diodes arranged outside the edge of the screen.

• On the other hand, backlit LEDs (better known as Full Array Lighting) has the light-producing diodes behind the screen.

• Full Array Lighting offers more control over the brightness of the image as these diodes can be independently controlled.

LCD:

• LCD stands for liquid crystal display.

• LCD panels are made of two layers of transparent material which are polarized and are glued together.

• One of the layers is coated with a special polymer that holds the individual liquid crystals.

• Current is then passed through individual crystals which allow the crystals to pass or block light to create images.

• LCD crystals do not produce their own light, so an external light source, such as florescent (CCFL/HCFL) or LEDs are needed for the image created by the LCD to become visible to the viewer.

• Currently almost all LCD TVs use LED light sources instead of a fluorescent light source.

• Unlike standard CRT and Plasma TV, since there are no phosphors that light up, less power is needed for operation and the light source in an LCD TV generates less heat than a Plasma or CRT TV.

• Also, because of the nature of LCD technology, there is no radiation emitted from the screen itself.