Large-screen television technology

"TV technology" redirects here. For the trade journal, see TV Technology.
Further information: History of display technology
56 inch DLP rear-projection TV

Large-screen television technology developed rapidly in the late 1990s and 2000s. Various thin screen technologies are being developed, but only the liquid crystal display (LCD), plasma display (PDP) and Digital Light Processing (DLP) have been released on the public market. These technologies have almost completely displaced cathode ray tubes (CRT) in television sales, due to the necessary bulkiness of cathode ray tubes. However, recently released technologies like organic light-emitting diode (OLED) and not-yet released technologies like surface-conduction electron-emitter display (SED) or field emission display (FED) are making their way to replace the first flat screen technologies in picture quality. The diagonal screen size of a CRT television is limited to about 40 inches because of the size requirements of the cathode ray tube, which fires three beams of electrons onto the screen, creating a viewable image. A larger screen size requires a longer tube, making a CRT television with a large screen (50 to 80 inches) unrealistic because of size. The aforementioned technologies can produce large-screen televisions that are much thinner.

Viewing distances

Horizontal, vertical and diagonal field of view

Before deciding on a particular display technology size, it is very important to calculate at what distances it is going to be viewed from. As the display size increases so does the ideal viewing distance. Bernard J. Lechner, while working for RCA, studied the best viewing distances for various conditions and derived the so-called Lechner distance.

As a rule of thumb, the viewing distance should be roughly two to three times the screen size for standard definition (SD) displays.[1][2][3][4][5]

Screen size (in) Viewing distance (ft) Viewing distance (m)
15–26 5–8 1.5-2.4
26–32 8–11.5 2.4-3.5
32–42 11.5–13 3.5-4
42–55 >13 >4

Display specifications

The following are important factors for evaluating television displays:

Display technologies

LCD television

Main article: LCD television

A pixel on an LCD consists of multiple layers of components: two polarizing filters, two glass plates with electrodes, and liquid crystal molecules. The liquid crystals are sandwiched between the glass plates and are in direct contact with the electrodes. The two polarizing filters are the outer layers in this structure. The polarity of one of these filters is oriented horizontally, while the polarity of the other filter is oriented vertically. The electrodes are treated with a layer of polymer to control the alignment of liquid crystal molecules in a particular direction. These rod-like molecules are arranged to match the horizontal orientation on one side and the vertical orientation on the other, giving the molecules a twisted, helical structure. Twisted nematic liquid crystals are naturally twisted, and are commonly used for LCD’s because they react predictably to temperature variation and electric current.

When the liquid crystal material is in its natural state, light passing through the first filter will be rotated (in terms of polarity) by the twisted molecule structure, which allows the light to pass through the second filter. When voltage is applied across the electrodes, the liquid crystal structure is untwisted to an extent determined by the amount of voltage. A sufficiently large voltage will cause the molecules to untwist completely, such that the polarity of any light passing through will not be rotated and will instead be perpendicular to the filter polarity. This filter will block the passage of light because of the difference in polarity orientation, and the resulting pixel will be black. The amount of light allowed to pass through at each pixel can be controlled by varying the corresponding voltage accordingly. In a color LCD each pixel consists of red, green, and blue subpixels, which require appropriate color filters in addition to the components mentioned previously. Each subpixel can be controlled individually to display a large range of possible colors for a particular pixel.

The electrodes on one side of the LCD are arranged in columns, while the electrodes on the other side are arranged in rows, forming a large matrix that controls every pixel. Each pixel is designated a unique row-column combination, and the pixel can be accessed by the control circuits using this combination. These circuits send charge down the appropriate row and column, effectively applying a voltage across the electrodes at a given pixel. Simple LCD’s such as those on digital watches can operate on what is called a passive-matrix structure, in which each pixel is addressed one at a time. This results in extremely slow response times and poor voltage control. A voltage applied to one pixel can cause the liquid crystals at surrounding pixels to untwist undesirably, resulting in fuzziness and poor contrast in this area of the image. LCD’s with high resolutions, such as large-screen LCD televisions, require an active-matrix structure. This structure is a matrix of thin-film transistors, each corresponding to one pixel on the display. The switching ability of the transistors allows each pixel to be accessed individually and precisely, without affecting nearby pixels. Each transistor also acts as a capacitor while leaking very little current, so it can effectively store the charge while the display is being refreshed.

The following are types of LC display technologies:

Plasma display

Main article: Plasma display
Composition of plasma display panel

A plasma display is made up of many thousands of gas-filled cells that are sandwiched in between two glass plates, two sets of electrodes, dielectric material, and protective layers. The address electrodes are arranged vertically between the rear glass plate and a protective layer. This structure sits behind the cells in the rear of the display, with the protective layer in direct contact with the cells. On the front side of the display there are horizontal display electrodes that sit in between a magnesium-oxide (MgO) protective layer and an insulating dielectric layer. The MgO layer is in direct contact with the cells and the dielectric layer is in direct contact with the front glass plate. The horizontal and vertical electrodes form a grid from which each individual cell can be accessed. Each individual cell is walled off from surrounding cells so that activity in one cell does not affect another. The cell structure is similar to a honeycomb structure except with rectangular cells.[6][7][8][9]

To illuminate a particular cell, the electrodes that intersect at the cell are charged by control circuitry and electric current flows through the cell, stimulating the gas (typically xenon and neon) atoms inside the cell. These ionized gas atoms, or plasmas, then release ultraviolet photons that interact with a phosphor material on the inside wall of the cell. The phosphor atoms are stimulated and electrons jump to higher energy levels. When these electrons return to their natural state, energy is released in the form of visible light. Every pixel on the display is made up of three subpixel cells. One subpixel cell is coated with red phosphor, another is coated with green phosphor, and the third cell is coated with blue phosphor. Light emitted from the subpixel cells is blended together to create an overall color for the pixel. The control circuitry can manipulate the intensity of light emitted from each cell, and therefore can produce a large gamut of colors. Light from each cell can be controlled and changed rapidly to produce a high-quality moving picture.[10][11][12][13]

Projection television

Main article: Video projector

A projection television uses a projector to create a small image from a video signal and magnify this image onto a viewable screen. The projector uses a bright beam of light and a lens system to project the image to a much larger size. A front-projection television uses a projector that is separate from the screen which could be a suitably prepared wall, and the projector is placed in front of the screen. The setup of a rear-projection television is in some ways similar to that of a traditional television, the projector is contained inside the television box and projects the image from behind the screen.

Rear-projection television

The following are different types of rear-projection televisions, which differ based on the type of projector and how the image (before projection) is created:

Laser Phosphor Display

In Laser Phosphor Display technology, first demonstrated in June 2010 at InfoComm, the image is provided by the use of lasers, which are located on the back of the television, reflected off a rapidly moving bank of mirrors to excite pixels on the television screen in a similar way to cathode ray tubes. The mirrors reflect the laser beams across the screen and so produce the necessary number of image lines. The small layers of phosphors inside the glass emit red, green or blue light when excited by a soft UV laser. The laser can be varied in intensity or completely turned on or off without a problem, which means that a dark display would need less power to project its images.

According to Prysm, the brightness and color range of the LPD exceeds LCD and LED technologies. It also has a viewing angle of almost 180˚. Its frequency lies near 240 Hz and it has a 1.6 mm dot pitch. Both of these aspects are claimed to exceed the current technologies such as LED. It is also claimed that unlike most other imaging technologies, the LPD images have no motion blur or flicker. In addition, LPD is said to be eco-friendly throughout its manufacture.

Comparison of television display technologies


Main article: Cathode Ray Tube

Though large-screen CRT TVs/monitors exist, but the screen size is limited because they may be impractical. The bigger the screen, the more the weight, and deeper the CRT. A typical 32-inch television can weigh about 50 lbs or more. The biggest ever CRT was about 60 inches, weighed 250 lbs. SlimFit televisions (40 inch, 80 lbs) exist, but this is not so common.



Plasma display


Projection television

Front-projection television


Rear-projection television


Comparison of different types of rear-projection televisions

CRT projector

Main article: CRT projector



LCD projector

Main article: LCD projector



DLP projector



See also


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