Flat screen

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Flat screen ( TFT ) for computers

A flat panel display is a screen that has a shallow depth. Flat panel displays are the imaging part of many electronic products such as televisions , computer monitors , notebooks , cell phones, and cameras . Flat screens can be manufactured according to various technical principles. LCD and OLED are currently widespread . Other technologies such as Mirasol and FED are used for special applications. Large-area flat screens, in particular LCD flat screens, have almost completely displaced cathode ray tube screens (CRT ) from the market due to their smaller dimensions, mass and energy consumption .

historical development

Details of the historical development of the different technologies for screens are described in the corresponding articles: plasma screen , liquid crystal display and organic light-emitting diode .

Parameters

Flat screens are characterized by:

A pivot function available on some screens is used to rotate the screen by 90 ° (portrait instead of wide format). The power consumption of a 24 ″ LCD is around 20 watts , an LCD television with a diagonal of 90 cm requires around 35 watts.

Designs

Flat screen as a television

There are several basic techniques that allow for shallow depth:

Plasma screens

Plasma screens were one way of realizing flat screens. Even if they look like LC displays , the way they work - igniting noble gases to light them up - is different.

Because of their luminosity, they represented an alternative for large displays. Due to their high power consumption and poor usability for small displays, they are no competition in the mobile sector. They also lose a lot of brightness after around 3 years of operation. This is especially true for older devices. Newer plasma screens were significantly cheaper in terms of energy consumption and have a service life that is identical to modern LC displays. Plasma screens are no longer produced today.

Liquid crystal displays

Most LCD flat screens are controlled via a thin-film transistor matrix in order to achieve sufficient resolution. LCD flat panels replaced screens with plasma displays from the 1980s. Initially, cell phones were equipped with LCDs. For this, as for other small battery-operated devices, plasma displays were out of the question.

OLEDs

OLEDs ( Organic Light Emitting Diode ) are one of the technologies that replace LCDs for certain applications. They are thin sheets of glass or plastic films that are printed with organic compounds (polymer compounds) using ink-jet technology (printing principle as in an inkjet printer) and then sealed. Suitable semiconductor components stimulate OLEDs to glow. Extremely thin, they can be used practically anywhere. The biggest problem with OLEDs was their high sensitivity to oxygen and moisture, which decompose the polymeric material through chemical reactions and limit its service life.

Further

Native screen resolution

Due to their design, flat screens generally only have a single screen resolution - with a few exceptions. Only in this is the display sharp to the pixel. This image resolution is referred to as native screen resolution or also as native display resolution; it is specified by the manufacturer in the trade name. All other resolutions must be converted to this native display resolution using scaling before they can be displayed on the flat screen. This process generally leads to image blurring with different resolutions.

Advantages and disadvantages

advantages

  • A lossless image can be transmitted through digital control via DVI , HDMI or DisplayPort .
  • When digitally controlled with the native image resolution, the image reproduction is considerably sharper than that of a CRT .
  • Flat screens are more compact and lighter due to the non-existent glass tube. Therefore, the technology can be used in mobile devices much more easily.
  • Due to their very shallow depth, they can be set up more easily at eye-friendly distances of around 1.5 × screen diagonals.
  • Flat screens of the type LCD have a significantly lower energy consumption for static images, as they predominate in computer applications.
  • They are not as strongly affected by a permanent same picture as (but are now less sensitive than at the time of CRT monitors screensavers were introduced to a burn to prevent images in the phosphor screen).
  • Disposal is less of a problem, with the backlight often containing environmentally hazardous mercury when using cold light cathodes .
  • LCD-TFT flat screens do not generate any X-rays and are largely insensitive to electrical and magnetic fields.

disadvantage

  • Compared to CRT monitors, LCD flat screens have a much lower response speed. This can lead to streaks when moving quickly and changing images. Even with the overdrive technology used in newer LCDs , the level of a CRT cannot be achieved.
  • They have a fixed resolution. Other resolutions that are not an integral multiple - e.g. B. 800 × 600 with native resolution 1600 × 1200 - the physical resolution must be interpolated and thus appear blurred. In contrast to CRT screens, no loss-free individual screen display is possible by selecting any graphics card resolution.

Depending on the technology of the flat screen, there are very different further disadvantages. With the currently most widespread technology of LCD screens, these are in particular the following:

  • They achieve poorer contrast ratios than CRT screens.
  • They have poorer brightness values.
  • You cannot display "real" black because the backlight is always active. LCD flat screens that have image content-controlled dynamic LED backlighting have improved black display. OLEDs, on the other hand, can display “real” black.
  • The image quality is more or less dependent on the viewing angle depending on the panel technology used.
  • The surface consists of soft, roughened plastic and is therefore dirt-attracting, difficult to clean, chemically sensitive and not scratch-resistant in contrast to picture tubes, which were all made of glass.
  • They can easily fall over or be knocked over (wind) in contrast to the massive and compact picture tube devices

Disposal health and safety

Older LCD flat screens with fluorescent tubes - backlighting may contain mercury . This is not the case with the LED backlights currently in use. When manually dismantling the fluorescent tubes, mercury can be released, which can pose an inhalation hazard to employees . The employer must therefore carry out a risk assessment. The risk assessment recommendations of the accident insurance institutions (EGU) provide practical information on risk assessment so that the limit values ​​for mercury are complied with. These include the workplace limit value (AGW), the short-term value according to TRGS 900 and the biological limit value (BGW) according to TRGS 903. If the process parameters and the protective measures described are complied with, it can be assumed that the minimization requirement according to Section 7 (4) of the GefStoffV will be met . Other hazardous substances such as dusts and dust constituents may have to be considered separately in the risk assessment.

Market shares

In 2009, according to a study by the market research institute EITO and based on the GfK market figures, over 8.3 million flat-screen televisions were sold in Germany, over a million of which were sold online. The focus of sales was on electronics retailers.

Word explanation

The word flat screen is actually wrong linguistically: The term flat in flat screens essentially refers to the depth of the housing and less to the fact that the screen surface is flat. There are also flat screen surfaces with CRTs. Furthermore, it is actually wrong to refer to the entire device as a screen , since the screen is only the image-displaying surface.

literature

Web links

Wiktionary: Flat screen  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ↑ a b c d e f g h i j Principle of LCD-TFT flat screens. In: Detlef Mietke, elektroniktutor.de. December 31, 2018, accessed August 27, 2019 .
  2. ↑ a b c d e f g h i j Flat screen test 2019: The best flat screens in comparison. In: Johanna Schweizer, Kaufberaterio Media LLC, Albuquerque, USA. May 20, 2019, accessed August 27, 2019 .
  3. ↑ German statutory accident insurance e. V. (DGUV): DGUV Information 213-733 - Recommendations for risk assessment by the accident insurance carriers (EGU) according to the Hazardous Substances Ordinance - Mercury exposure when dismantling flat screens. Retrieved November 5, 2019 .
  4. ↑ Marc Thylmann: One million flat screen televisions sold on the web. In: pressebox.de. Bitkom e. V., June 25, 2010, accessed June 17, 2016 .
  5. ↑ p4c.philips.com
  6. ↑ asianic.com.ph