LED television

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LED televisions are televisions that use light-emitting diodes (LEDs) either for backlighting or to generate the image itself.

The following definition of terms also applies to most computer monitors that use very similar technology to display images. Most is LC - displays (LCDs), the backlight LEDs is (see LED backlight ). For this purpose, both white and colored light-emitting diodes that can be mixed with white are used, which are arranged behind the liquid crystal display. The term “LED television” is misleading for this type of display technology, but it is common. Correctly, such devices should be referred to as "LED-backlit LCD televisions".

Disambiguation

Comparison diagram LCD / LED
LED strips in a 40 inch TV. (Without white reflector film and the scatter films between the LCD panel and the LED strip, production status 2016.)

Up until around 2008, only three different home use technologies were essentially available, namely liquid crystal displays , plasma displays and projection displays . Because liquid crystal displays only modulate the light; That is, how light valves work and do not emit any light themselves, flat lighting is installed behind the liquid crystal display for televisions in order to display the image information in transmitted light (transmission). In the simplified diagram opposite, such liquid crystal screens are designated as display types A and B, the liquid crystal display 1 modulating the light in accordance with the image to be displayed.

LED televisions (English LED TV ) and LED monitors have been advertised in the trade since around 2009 (diagram display type B). Up until 2013, practically all cases were the previous liquid crystal displays for image generation . The only new thing is the backlighting of these LCD televisions using light-emitting diodes ( LEDs ; scheme: part 3, with a light distributor (not shown) providing extensive illumination).

Comparison of backlighting techniques

Until around 2008, cold cathode tubes ( fluorescent tubes ) were used almost exclusively as background lighting in LCD televisions (scheme: Part 2 in combination with a flat light distributor, not shown). The use of LEDs (scheme: part 3) instead of fluorescent tubes is emphasized in product advertising because it has the following advantages over the previous technology:

  • more compact design with less depth of the device
  • lower power consumption at lower electrical voltages
  • shorter switching times (see dynamic light-emitting diode control)
  • less decrease in light intensity and change in color spectrum in the course of use
  • higher reliability and service life.

Use of RGB combinations

Additional advantages result from special versions of the light-emitting diodes: Here, several red-green-blue-light-emitting diode combinations are attached distributed behind the display surface ( additive color mixing , full-array LED ). This type of lighting, matched to the color filters of the liquid crystal display, gives the television a better color spectrum, but is more expensive than using light-emitting diodes along the screen periphery ( edge-lit ).

Quantum dots for an optimal color spectrum

Using Nano semiconductor crystals ( quantum dots , engl. Quantum dots ) coated on a glass plate or film, and (as of GaN z.) By blue, short-wavelength LEDs is irradiated from behind, the spectrum of the backlight of LCD can be applied to an unprecedented Type (technical term extended color space ). This form of fluorescence technology is being further developed in various laboratories. The US company 3M, a major supplier of backlighting components for LCDs, is working with Nanosys, Inc. on appropriately coated films. The British company Nanoco Group PLC has also been active in the further development of quantum dots for several years and has concluded cooperation agreements with Asian manufacturers of liquid crystal displays and OLEDs . The US company QD Vision also works with Asian companies that optimize the background lighting of LC displays. The same applies to the Swiss company Avantama, which developed and manufactured quantum dots only later, but which do not contain any toxic cadmium and are based on nanocrystals with a perovskite structure .

In 2013, Sony was the first company to bring certain high-quality LCD televisions with LED backlighting optimized in this way to the market under the name Triluminos , which was previously used . The light from blue LEDs on a pane of glass or foil attached in front of it is converted into very pure, narrow-band blue, green and red by different quantum dots . The combination of these three basic colors creates an optimal white illumination of the LC display from behind. Since then, the Korean companies Samsung Electronics , LG Electronics and Chinese television manufacturers ( TCL , Changhong, Hisense) have improved LCD televisions with LED backlighting with a quantum dot layer and presented them at the 2015 CES trade fair. In 2016, Samsung Electronics decided to re-market their high-quality televisions with the name QLED in order to draw attention to the technology with quantum dots. This should also prepare the transition to the new screens with self-illuminating QLEDs , which are still being developed at Samsung .

Dynamic light emitting diode control depending on the image content

Previous liquid crystal screens have a limited contrast because the display of a black image point ( pixel ) was not completely dark due to the background lighting, which was still somewhat translucent. Through selective control of the distributed light-emitting diodes depending on the image content, dark parts can be made darker by the reduced local lighting ( local dimming ) and therefore the contrast can be increased. The number of light-emitting diodes attached in a distributed manner (scheme B: Part 3) is much smaller than the number of pixels in the liquid crystal display. Therefore, the aforementioned increase in contrast cannot be achieved individually for each pixel, but only for a larger group of neighboring pixels. Nevertheless, the best contrast of all LCD televisions can be achieved with this technology. However, only a few devices are commercially available with this relatively expensive backlight as a combination of full-array LEDs with local dimming .

Real LED displays with monolithic light emitting diodes

MK38527 LED Display: Real LED display. The picture shows a matrix with red, green and blue light emitting diodes.

Inorganic, monolithically produced, single-crystal light-emitting diodes have been used as display elements since the early 1970s. Examples were the PULSAR wristwatches with a red digital display and the first pocket calculator . Many details and information can be found in the article LED . A breakthrough came with the development of blue LEDs, because they made it possible to combine LEDs to generate white light.

Monolithic LEDs are produced on monocrystalline semiconductor discs ( wafers ). These round disks made by growing crystals now have a diameter of up to 30 cm. If all the remaining problems were solved, it would not be able to make larger monolithic LED screens. In practice, individual LEDs are obtained from this by cutting the pane and making individual electrical contacts.

Large screens outdoors (e.g. in football stadiums, video wall ) are implemented with a large number of individual light-emitting diodes.

So-called micro-LED displays are taking a new approach . Micro-LED arrangements are also produced monolithically in a batch process on a suitable substrate made of sapphire or silicon . The preferred material is inorganic, monocrystalline gallium nitride (GaN), which is epitaxially formed on the substrate. In contrast to the previous production, however, the light-emitting diodes are not subsequently cut, but kept as a display matrix. The necessary novel structure with multiple challenges such as doping for different colors, contacting as a matrix arrangement, mechanical stability during transfer from the manufacturing substrate to a display substrate have not yet been solved in such a way that such displays can be used for commercial products. The company Apple Inc. sees potential in this new technology and, therefore, the pioneering company has LuxVue Technology adopted.

Giant television screens with light-emitting diodes as self-illuminating pixels have been around since light-emitting diodes in the colors red, green and blue were produced in large numbers. High-resolution displays with structure widths that are significantly smaller have only been commercially produced for some time. Around 2018, the first LED cinema screens for commercial use by the Samsung company were spreading in Germany; this is a modular 10.3 by 5.4 meter screen with a UHD image resolution.

Displays with organic light emitting diodes (OLEDs)

Electroluminescence in layers of organic material has been researched since the 1950s . In the meantime, organic semiconductor materials have been developed as OLEDs , which are suitable as display elements in thin-film technology . This technique is shown in simplified form in the diagram as display type C. The OLEDs 4 are applied so densely on a substrate (or between two substrates) using thin-film technology that they serve as individual pixels for image generation. Advantages over liquid crystal displays are:

  • OLEDs emit light themselves, so they do not need backlighting and offer high contrast.
  • Potentially lower manufacturing costs for large screens than in 2017 and lower power consumption when using the manufacturing process using a metal mask
  • OLEDs can emit light in different colors, while LCDs require additional color filters.
  • less angle dependence when viewing
  • shorter electro-optical response times.

The most important disadvantage is the limited service life. Further disadvantages are the UV sensitivity and the currently still high production costs. Samsung Electronics, as a major manufacturer of both liquid crystal and OLED displays, decided in 2016 to forego OLEDs for future large-format televisions. In addition to the disadvantages mentioned, the burn-in of certain patterns is also mentioned as a further disadvantage in OLEDs. In contrast to the competition, the manufacturer uses QLEDs instead of OLEDs in television technology.

Many small to medium-sized portable devices such as digital cameras, smartphones (e.g. Samsung Galaxy S), tablets and laptops are equipped with such displays. In January 2012, the first prototypes of 55-inch OLED televisions from LG Display and Samsung were shown at the Consumer Electronics Show (CES) in Las Vegas . OLED screens have now become widely available on large format televisions. These displays are often summarized under the term AMOLED ( active-matrix organic light emitting diode ).

Individual evidence

  1. ↑ Patent US4096550 : Illuminating Arrangement for a Field-Effect Liquid-Crystal Display as well as Fabrication and Application of the Illuminating Arrangement. Published on June 20, 1978 , inventor: Boller W., M. Donati, Fingerle J., Wild P
  2. ↑ http://www.ledtele.co.uk/ledvslcd.html LED vs LCD TV Comparison
  3. ↑ http://www.nanosysinc.com/what-we-do/display-backlighting/qdef-how-does-it-work/
  4. ↑ P. Patel: Quantum dots are behind new displays . In: IEEE Spectrum . tape 49 , no. 8 , 2012, p. 14-17 , doi : 10.1109 / MSPEC.2012.6247547 .
  5. ↑ QD Vision company with "Color IQ"
  6. ↑ Cadmium-free quantum dot display. Avantama.com. accessed on August 17, 2019
  7. ↑ Archived copy ( memento of the original dated August 9, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.chip.de
  8. ↑ https://www.heise.de/ct/ausgabe/2013-12-Nanopartikel-fuer-sattere-Display-Farben-2321302.html
  9. ^ Tekla Perry: CES 2015 - Placing the Bets on New TV Technologies. In: IEEE Spectrum online , January 7, 2015.
  10. ↑ Wolfgang Tunze: Color television reinvented. In: NZZ am Sonntag , January 11, 2015, p. 62
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  12. ↑ Geoffrey Morrison: How QLED TV could help Samsung beat LG's OLEDs. CNET News, June 30, 2016, accessed January 13, 2017.
  13. ↑ QLED versus OLED, Samsung is fueling system dispute in TV technology. Die Wirtschaftswoche , January 5, 2017, accessed on January 13, 2017
  14. ↑ Nick Holonyak, SF Bevacqua: Coherent (visible) light emission from Ga (As1-xPx) junctions . In: Applied Physics Letters . tape 1 , no. 4 , 1962, pp. 82 , doi : 10.1063 / 1.1753706 .
  15. ↑ Shuji Nakamura, Gerhard Fasol, Stephen J. Pearton: The Blue Laser Diode: The Complete Story. 2nd edition, Springer, 2000, ISBN 3-540-66505-6 .
  16. ^ Andreas Bibl et al .: Light emitting diode structure. U.S. Patent 8552436, published October 8, 2013
  17. ↑ David Murphy: Apple Acquires Micro-LED Display Maker LuxVue Technology . In: PC Mag . May 3, 2014.
  18. ↑ Alvaro Campos: Why Did Apple Inc Buy This Micro-LED Tech Startup? . 13th of May 2013.
  19. ↑ A. Bernanose, M. Comte, P. Vouaux: A new method of emission of light by certain organic compounds . In: Journal of Chemical Physics . tape 50 , 1953, pp. 64-68 .
  20. ↑ a b c Glory KJ Chen, Janglin Chen: AMOLED Manufacture. In: Handbook of Visual Display Technology. 2nd Edition. Springer-Verlag, Berlin / Heidelberg 2015, pages 4–6
  21. ↑ Marko Winzker: Electronics for decision-makers. Basic knowledge for business and technology . Wiesbaden 2017, p. 91.
  22. ↑ OLED TV estimated lifespan shorter then expected ( Memento from May 9, 2008 in the Internet Archive )
  23. ↑ Lee Gijong: Samsung Electronics to skip OLED TV and go straight to QLED TV. iPnomics, May 24, 2016; accessed January 11, 2017
  24. ↑ Wolfgang Tunze: All things that tick digitally. In: NZZ am Sonntag , January 8, 2017, p. 54.
  25. ↑ Mason Inman: OLED or QLED? . 5th January 2017. 
  26. ↑ CES 2012: Samsung counters LG's 55-inch OLED with its own 55-inch television , cnet.de