LED-backlit LCD

Last updated

An Apple iPod Touch disassembled to show the array of white-edge LEDs powered on with the device IPod Touch 2G Backlight.JPG
An Apple iPod Touch disassembled to show the array of white-edge LEDs powered on with the device

An LED-backlit LCD is a liquid-crystal display that uses LEDs for backlighting instead of traditional cold cathode fluorescent (CCFL) backlighting. [1] LED-backlit displays use the same TFT LCD (thin-film-transistor liquid-crystal display) technologies as CCFL-backlit LCDs, but offer a variety of advantages over them.

Contents

Televisions that use a combination of an LED backlight with an LCD panel are sometimes advertised as LED TVs, although they are not truly LED displays. [1] [2]

Backlit LCDs cannot achieve true blacks for pixels, unlike OLED and microLED displays. This is because even in the "off" state, black pixels still allow some light from the backlight through. Some LED-backlit LCDs use local dimming zones to increase contrast between bright and dim areas of the display, but this can result in a "blooming" or "halo" effect on dark pixels in or adjacent to an illuminated zone. [3]

Comparison with CCFL-backlit LCDs

Advantages

When compared with earlier CCFL backlights, using LEDs for backlighting offers:

LED arrangements

A single direct LED cluster of a LCD Medical Econet PalmCare - display module - LED-backlit LCD-1405.jpg
A single direct LED cluster of a LCD

LED backlights replace CCFL (fluorescent) lamps with a few to several hundred white, RGB or blue LEDs. An LCD with LED-Backlight may be edge- or direct-lit: [9]

Additionally a special diffusion panel (light guide plate, LGP) is often used to spread the light evenly behind the screen.

The local dimming method of backlighting allows to dynamically control the level of light intensity of specific areas of darkness on the screen, resulting in much higher dynamic-contrast ratios, though at the cost of less detail in small, bright objects on a dark background, such as star fields or shadow details. [10]

A 2016 study by the University of California (Berkeley) suggests that the subjectively perceived visual enhancement with common contrast source material levels off at about 60 LCD local dimming zones. [11]

Technology

LED-backlit LCDs are not self-illuminating (unlike pure-LED systems). There are several methods of backlighting an LCD panel using LEDs, including the use of either white or RGB (Red, Green, and Blue) LED arrays behind the panel and edge-LED lighting (which uses white LEDs around the inside frame of the TV and a light-diffusion panel to spread the light evenly behind the LCD panel). Variations in LED backlighting offer different benefits. The first commercial full-array LED-backlit LCD TV was the Sony Qualia 005 (introduced in 2004), which used RGB LED arrays to produce a color gamut about twice that of a conventional CCFL LCD television. This was possible because red, green and blue LEDs have sharp spectral peaks which (combined with the LCD panel filters) result in significantly less bleed-through to adjacent color channels. Unwanted bleed-through channels do not "whiten" the desired color as much, resulting in a larger gamut. RGB LED technology continues to be used on Sony BRAVIA LCD models. LED backlighting using white LEDs produces a broader spectrum source feeding the individual LCD panel filters (similar to CCFL sources), resulting in a more limited display gamut than RGB LEDs at lower cost.[ citation needed ]

Television sets described as "LED TVs" are LCD-based, with the LEDs dynamically controlled using the video information [12] (dynamic backlight control or dynamic "local dimming" LED backlight, also marketed as HDR, high dynamic range television, invented by Philips researchers Douglas Stanton, Martinus Stroomer and Adrianus de Vaan [13] [14] [15]

The evolution of energy standards and the increasing public expectations regarding power consumption made it necessary for backlight systems to manage their power. As for other consumer electronics products (e.g., fridges or light bulbs), energy consumption categories are enforced for television sets. [16] Standards for power ratings for TV sets have been introduced, e.g., in the US, EU, Australia, [17] and China. [18] A 2008 study [19] showed that among European countries power consumption is one of the most important criteria for consumers when they choose a television, as important as the screen size. [20]

Using PWM (pulse-width modulation), a technology where the intensity of the LEDs are kept constant but the brightness adjustment is achieved by varying a time interval of flashing these constant light intensity light sources, [21] the backlight is dimmed to the brightest color that appears on the screen while simultaneously boosting the LCD contrast to the maximum achievable levels, drastically increasing the perceived contrast ratio, increasing the dynamic range, improving the viewing angle dependency of the LCD and drastically reducing power consumption.[ clarification needed ]

The combination of LED dynamic backlight control [13] in combination with reflective polarizers and prismatic films (invented by Philips researchers Adrianus de Vaan and Paulus Schaareman [22] make these "LED" (LCD) televisions far more efficient than the previous CRT-based sets, leading to a worldwide energy saving of 600 TWh in 2017, equal to 10% of the electricity consumption of all households worldwide, or twice the energy production of all solar cells in the world. [23] [24]

The prismatic and reflective polarization films are generally achieved using so called DBEF films manufactured and supplied by 3M. [25] [26] These reflective polarization films using uniaxial oriented polymerized liquid crystals (birefringent polymers or birefringent glue) were invented in 1989 by Philips researchers Dirk Broer, Adrianus de Vaan and Joerg Brambring. [27]

A first dynamic "local dimming" LED backlight was public demonstrated by BrightSide Technologies in 2003, [28] and later commercially introduced for professional markets (such as video post-production). [29] Edge LED lighting was first introduced by Sony in September 2008 on the 40-inch (1,000 mm) BRAVIA KLV-40ZX1M (known as the ZX1 in Europe). Edge-LED lighting for LCDs allows thinner housing; the Sony BRAVIA KLV-40ZX1M is 1 cm thick, and others are also extremely thin.[ citation needed ]

LED-backlit LCDs have longer life and better energy efficiency than plasma and CCFL LCD TVs. [30] Unlike CCFL backlights, LEDs do not use mercury in their manufacture, which is an environmental pollutant. However, other elements (such as gallium and arsenic) are used in the manufacture of the LED emitters; there is debate over whether they are a better long-term solution to the problem of screen disposal.[ citation needed ]

Because LEDs can be switched on and off more quickly than CCFLs and can offer a higher light output, it is theoretically possible to offer very high contrast ratios. They can produce deep blacks (LEDs off) and high brightness (LEDs on). However, measurements made from pure-black and pure-white outputs are complicated by edge-LED lighting not allowing these outputs to be reproduced simultaneously on screen.[ clarification needed ]

Full-array mini-LED backlights, consisting of several thousand WLEDs, were being researched for TVs and mobile devices in 2017. [31]

The white LEDs in LED backlights may use special silicate phosphors, which are brighter but degrade faster. [32] The size of the LEDs is one of the factors that determines the size of the bezel of LED-backlit LCDs. [33]

Quantum dot enhancement film (QDEF)

Quantum dots are photoluminescent; they are useful in displays because they emit light in specific, narrow normal distributions of wavelengths. To generate white light best suited as an LCD backlight, parts of the light of a blue-emitting LED are transformed by quantum dots into small-bandwidth green and red light such that the combined white light allows a nearly ideal color gamut to be generated by the RGB color filters of the LCD panel. The quantum dots may be in a separate layer as a quantum dot enhancement film, or replace pigment-based green and red resists normally used in LCD color filters. In addition, efficiency is improved, as intermediate colors are no longer present and do not have to be filtered out by the color filters of the LCD screen. This can result in a display that more accurately renders colors in the visible spectrum. Companies developing quantum dot solutions for displays include Nanosys, 3M as a licensee of Nanosys, QD Vision of Lexington, Massachusetts, US and Avantama of Switzerland. [34] [35] This type of backlighting was demonstrated by various TV manufacturers at the Consumer Electronics Show 2015. [36] Samsung introduced their first 'QLED' quantum dot displays at CES 2017 and later formed the 'QLED Alliance' with Hisense and TCL to market the technology. [37] [38]

Mini LED

Mini LED displays are LED-backlit LCDs with mini-LED–based backlighting supporting over a thousand full array local dimming (FALD) zones, providing deeper blacks and a higher contrast ratio. [39] An example of a product that uses Mini LED backlighting is Apple's 2021 year 12.9 inch iPad Pro. [40]

Backlight-dimming flicker

LED backlights are often dimmed by applying pulse-width modulation to the supply current, switching the backlight off and on more quickly than the eye can perceive. If the dimming-pulse frequency is too low or the user is sensitive to flicker, this may cause discomfort and eyestrain similar to the flicker of CRT displays at lower refresh rates. [41] This can be tested by simply waving a hand in front of the screen; if it appears to have sharply-defined edges as it moves, the backlight is pulsing at a fairly low frequency. If the hand appears blurry, the display either has a continuously-illuminated backlight or is operating at a frequency too high to perceive. Flicker can be reduced (or eliminated) by setting the display to full brightness, although this can degrade image quality and increases power consumption.[ citation needed ]

See also

Related Research Articles

<span class="mw-page-title-main">Computer monitor</span> Computer output device

A computer monitor is an output device that displays information in pictorial or textual form. A discrete monitor comprises a visual display, support electronics, power supply, housing, electrical connectors, and external user controls.

<span class="mw-page-title-main">Liquid-crystal display</span> Display that uses the light-modulating properties of liquid crystals

A liquid-crystal display (LCD) is a flat-panel display or other electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers. Liquid crystals do not emit light directly but instead use a backlight or reflector to produce images in color or monochrome. LCDs are available to display arbitrary images or fixed images with low information content, which can be displayed or hidden: preset words, digits, and seven-segment displays are all examples of devices with these displays. They use the same basic technology, except that arbitrary images are made from a matrix of small pixels, while other displays have larger elements. LCDs can either be normally on (positive) or off (negative), depending on the polarizer arrangement. For example, a character positive LCD with a backlight will have black lettering on a background that is the color of the backlight, and a character negative LCD will have a black background with the letters being of the same color as the backlight.

<span class="mw-page-title-main">RGB color spaces</span> Any additive color space based on the RGB color model

An RGB color space is one of many specific additive colorimetric color spaces based on the RGB color model.

<span class="mw-page-title-main">Plasma display</span> Type of flat panel display

A plasma display panel (PDP) is a type of flat panel display that uses small cells containing plasma: ionized gas that responds to electric fields. Plasma televisions were the first large flat panel displays to be released to the public.

<span class="mw-page-title-main">Flat-panel display</span> Electronic display technology

A flat-panel display (FPD) is an electronic display used to display visual content such as text or images. It is present in consumer, medical, transportation, and industrial equipment.

<span class="mw-page-title-main">Gamut</span> Color reproduction capability

In color reproduction and colorimetry, a gamut, or color gamut, is a convex set containing the colors that can be accurately represented, i.e. reproduced by an output device or measured by an input device. Devices with a larger gamut can represent more colors. Similarly, gamut may also refer to the colors within a defined color space, which is not linked to a specific device. A trichromatic gamut is often visualized as a color triangle. A less common usage defines gamut as the subset of colors contained within an image, scene or video.

<span class="mw-page-title-main">Video projector</span> Device that projects video onto a surface

A video projector is an image projector that receives a video signal and projects the corresponding image onto a projection screen using a lens system. Video projectors use a very bright ultra-high-performance lamp, Xenon arc lamp, metal halide lamp, LED or solid state blue, RB, RGB or remote fiber-optic RGB lasers to provide the illumination required to project the image. Most modern projectors can correct any curves, blurriness and other inconsistencies through manual settings.

Flicker is a visible change in brightness between cycles displayed on video displays. It applies to the refresh interval on cathode ray tube (CRT) televisions and computer monitors, as well as plasma computer displays and televisions.

A television set or television receiver is an electronic device for the purpose of viewing and hearing television broadcasts, or as a computer monitor. It combines a tuner, display, and loudspeakers. Introduced in the late 1920s in mechanical form, television sets became a popular consumer product after World War II in electronic form, using cathode ray tube (CRT) technology. The addition of color to broadcast television after 1953 further increased the popularity of television sets in the 1960s, and an outdoor antenna became a common feature of suburban homes. The ubiquitous television set became the display device for the first recorded media for consumer use in the 1970s, such as Betamax, VHS; these were later succeeded by DVD. It has been used as a display device since the first generation of home computers and dedicated video game consoles in the 1980s. By the early 2010s, flat-panel television incorporating liquid-crystal display (LCD) technology, especially LED-backlit LCD technology, largely replaced CRT and other display technologies. Modern flat panel TVs are typically capable of high-definition display and can also play content from a USB device. Starting in the late 2010s, most flat panel TVs began to offer 4K and 8K resolutions.

<span class="mw-page-title-main">LCD television</span> Television set with liquid-crystal display

A liquid-crystal-display television is a television set that uses a liquid-crystal display to produce images. It is by far the most widely produced and sold type of television display. LCD TVs are thin and light, but have some disadvantages compared to other display types such as high power consumption, poorer contrast ratio, and inferior color gamut.

The contrast ratio (CR) is a property of a display system, defined as the ratio of the luminance of the brightest shade (white) to that of the darkest shade (black) that the system is capable of producing. A high contrast ratio is a desired aspect of any display. It has similarities with dynamic range.

Nanosys is a nanotechnology company located in Milpitas, California and founded in 2001. The company develops and manufactures quantum dot materials for display products.

<span class="mw-page-title-main">Backlight</span> Form of illumination used in liquid crystal displays

A backlight is a form of illumination used in liquid-crystal displays (LCDs) that illuminates an LCD from the side or back of a display panel. LCDs do not produce light by themselves, so they need illumination to produce a visible image. Backlights are often used in smartphones, computer monitors, and LCD televisions. They are used in small displays to increase readability in low light conditions such as in wristwatches. Typical sources of light for backlights include light-emitting diodes (LEDs) and cold cathode fluorescent lamps (CCFLs).

A thin-film-transistor liquid-crystal display is a type of liquid-crystal display that uses thin-film-transistor technology to improve image qualities such as addressability and contrast. A TFT LCD is an active matrix LCD, in contrast to passive matrix LCDs or simple, direct-driven LCDs with a few segments.

This is a comparison of various properties of different display technologies.

XBR is a line of LCD, OLED, Plasma, Rear Projection, and CRT televisions produced by Sony. According to Sony, XBR is an acronym for eXtended Bit Rate, although there is evidence that it originally stood for "Project X, Black Remote" which was supposed to set it apart from the then-standard line of Sony televisions. The XBR range is typically derived from equipment that has been released in Japan and Europe as mid and high-end models, usually with some small upgrades. For example, in Europe and Japan, the Sony X-Series 1080p TVs had two HDMI inputs, whereas on the American XBR version, there were three. Some XBR televisions may cost up to $25,000 USD.

<span class="mw-page-title-main">Large-screen television technology</span> Technology rapidly developed in the late 1990s and 2000s

Large-screen television technology developed rapidly in the late 1990s and 2000s. Prior to the development of thin-screen technologies, rear-projection television was standard for larger displays, and jumbotron, a non-projection video display technology, was used at stadiums and concerts. Various thin-screen technologies are being developed, but only liquid crystal display (LCD), plasma display (PDP) and Digital Light Processing (DLP) have been publicly released. Recent technologies like organic light-emitting diode (OLED) as well as not-yet-released technologies like surface-conduction electron-emitter display (SED) or field emission display (FED) are in development to replace earlier flat-screen technologies in picture quality.

Contrast in visual perception is a felt difference in appearance of two or more parts of a field seen simultaneously or successively.

<span class="mw-page-title-main">Quantum dot display</span> Type of display device

A quantum dot display is a display device that uses quantum dots (QD), semiconductor nanocrystals which can produce pure monochromatic red, green, and blue light. Photo-emissive quantum dot particles are used in LCD backlights or display color filters. Quantum dots are excited by the blue light from the display panel to emit pure basic colors, which reduces light losses and color crosstalk in color filters, improving display brightness and color gamut. Light travels through QD layer film and traditional RGB filters made from color pigments, or through QD filters with red/green QD color converters and blue passthrough. Although the QD color filter technology is primarily used in LED-backlit LCDs, it is applicable to other display technologies which use color filters, such as blue/UV active-matrix organic light-emitting diode (AMOLED) or QNED/MicroLED display panels. LED-backlit LCDs are the main application of photo-emissive quantum dots, though blue OLED panels with QD color filters are being researched.

Standard-dynamic-range video is a video technology which represents light intensity based on the brightness, contrast and color characteristics and limitations of a cathode ray tube (CRT) display. SDR video is able to represent a video or picture's colors with a maximum luminance around 100 cd/m2, a black level around 0.1 cd/m2 and Rec.709 / sRGB color gamut. It uses the gamma curve as its electro-optical transfer function.

References

  1. 1 2 "LED vs LCD TV Comparison". Archived from the original on 20 May 2017. Retrieved 28 November 2009.
  2. ↑ Practice, Advertising Standards Authority | Committee of Advertising. "Samsung Electronics (UK) Ltd". asa.org.uk.{{cite web}}: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link)
  3. ↑ Shafer, Rob (11 June 2022). "What Is FALD Blooming Or Halo Effect?". DisplayNinja. Retrieved 13 February 2023.
  4. ↑ Dell Studio XPS 16: Highest Color Gamut Ever?. Anandtech.com, 26 February 2009
  5. ↑ Competing display technologies for the best image performance; A.J.S.M. de Vaan; Journal of the society of information displays, Volume 15, Issue 9 September 2007 Pages 657–666; http://onlinelibrary.wiley.com/doi/10.1889/1.2785199/abstract?
  6. ↑ Novitsky, Tom; Abbott, Bill (12 November 2007). "Driving LEDs versus CCFLs for LCD backlighting". EE Times. Archived from the original on 28 November 2010. Retrieved 21 November 2020.
  7. ↑ Dimming options for LCD brightness; J. Moronski; Electronicproducts.com; 3 January 2004; http://www.electronicproducts.com/Optoelectronics/Dimming_options_for_LCD_brightness_control.aspx
  8. ↑ "Plasma Vs LCD vs LED TV". Archived from the original on 10 July 2012. Retrieved 1 October 2011.
  9. ↑ "Local Dimming on TVs: Direct-Lit, Full-Array, and Edge-Lit". RTINGS.com. Retrieved 10 September 2023.
  10. ↑ Scott Wilkinson. "Ultimate Vizio Archived 26 August 2009 at the Wayback Machine ". UltimateAVmag.com. Posted Fri 29 May 2009. Retrieved 16 December 2009.
  11. ↑ David M. Hoffman, Natalie Stepien, Wei Xiong "Implications of the number of local dimming zones and native LCD contrast on visual quality of HDR displays
  12. ↑ LED TVs: 10 things you need to know; David Carnoy, David Katzmaier; CNET.com/news; 3 June 2010; https://www.cnet.com/news/led-tvs-10-things-you-need-to-know/
  13. 1 2 Method of and device for generating an image having a desired brightness; D.A. Stanton; M.V.C. Stroomer; A.J.S.M. de Vaan; US patent USRE42428E; 7 June 2011; https://worldwide.espacenet.com/publicationDetails/biblio?CC=US&NR=RE42428E
  14. ↑ LED local dimming explained; G. Morrison, CNET.com/news, 26 March 2016
  15. ↑ Chen, Haiwei; Zhu, Ruidong; Li, Ming-Chun; Lee, Seok-Lyul; Wu, Shin-Tson (24 January 2017). "Pixel-by-pixel local dimming for high-dynamic-range liquid crystal displays". Optics Express. 25 (3): 1973–1984. Bibcode:2017OExpr..25.1973C. doi: 10.1364/oe.25.001973 . ISSN   1094-4087. PMID   29519046.
  16. ↑ Commission Regulation (EC) No 642/2009 of 22 July 2009 implementing Directive 2005/32/EC of the European Parliament and of the Council with regard to ecodesign requirements for televisions
  17. ↑ "EU Australia and US regulation on energy consumption in TV sets", 2008
  18. ↑ "China Regulation on Energy Consumption in TV Sets", 2010
  19. ↑ "International survey on the importance of the energy efficiency of TV appliances", 2008
  20. ↑ Controlling Power Consumption for Displays With Backlight Dimming; Claire Mantel et al; Journal of Display Technology; Volume: 9, Issue: 12, Dec. 2013; https://ieeexplore.ieee.org/document/6520956
  21. ↑ Dimming options for LCD brightness; J. Moronski; Electronicproducts.com; 3 Januari 2004; http://www.electronicproducts.com/Optoelectronics/Dimming_options_for_LCD_brightness_control.aspx
  22. ↑ Illumination system and display device including such a system; A.J.S.M. de Vaan; P.B. Schaareman; European patent EP0606939B1; https://worldwide.espacenet.com/publicationDetails/biblio?CC=EP&NR=0606939B1&KC=B1&FT=D&ND=5&date=19980506&DB=EPODOC&locale=en_EP#
  23. ↑ Energy Efficiency Success Story: TV Energy Consumption Shrinks as Screen Size and Performance Grow, Finds New CTA Study; Consumer Technology Association; press release 12 July 2017; https://cta.tech/News/Press-Releases/2017/July/Energy-Efficiency-Success-Story-TV-Energy-Consump.aspx Archived 4 November 2017 at the Wayback Machine
  24. ↑ LCD Television Power Draw Trends from 2003 to 2015; B. Urban and K. Roth; Fraunhofer USA Center for Sustainable Energy Systems; Final Report to the Consumer Technology Association; May 2017; http://www.cta.tech/cta/media/policyImages/policyPDFs/Fraunhofer-LCD-TV-Power-Draw-Trends-FINAL.pdf Archived 1 August 2017 at the Wayback Machine
  25. ↑ Brochure 3M Display Materials & Systems Division Solutions for Large Displays: The right look matters; http://multimedia.3m.com/mws/media/977332O/display-materials-systems-strategies-for-large-displays.pdf
  26. ↑ Broadband reflective polarizers based on form birefringence for ultra-thin liquid crystal displays; S.U. Pan; L. Tan and H.S. Kwok; Vol. 25, No. 15; 24 July 2017; Optics Express 17499; https://www.osapublishing.org/oe/viewmedia.cfm?uri=oe-25-15-17499&seq=0
  27. ↑ Polarisation-sensitive beam splitter; D.J. Broer; A.J.S.M. de Vaan; J. Brambring; European patent EP0428213B1; 27 July 1994; https://worldwide.espacenet.com/publicationDetails/biblio?CC=EP&NR=0428213B1&KC=B1&FT=D#
  28. ↑ H. Seetzen, et al.: "A High Dynamic Range Display System Using Low and High Resolution Modulators", SID03 Digest
  29. ↑ "BrightSide DR37-P HDR display | bit-tech.net". bit-tech.net.
  30. ↑ "Samsung.com". Samsung.com. Retrieved 17 May 2009.
  31. ↑ "Mini LED TV Backlight and Display to Be Rolled Out Soon". ledinside.com.
  32. ↑ Bush, Steve (14 March 2014). "Discussing LED lighting phosphors".
  33. ↑ "New report explains how Apple will eliminate the bezel on its 2018 LCD iPhone". 10 July 2018.
  34. ↑ Cadmium-free quantum dot display. avantama.com. Retrieved 16 August 2019
  35. ↑ IEEE Spectrum, 2012, 8, p.11-12 Quantum Dots Are Behind New Displays
  36. ↑ CES 2015 - Placing bets on the New TV Technologies. IEEE Spectrum, 7 January 2015. Retrieved 12 January 2015
  37. ↑ "Samsung, Hisense & TCL form 'QLED Alliance' to take on OLED - FlatpanelsHD".
  38. ↑ "QLED Alliance Kicks off in Beijing". 18 April 2017.
  39. ↑ Shafer, Rob (5 June 2019). "Mini-LED vs MicroLED - What Is The Difference? [Simple Explanation]". DisplayNinja. Retrieved 14 September 2019.
  40. ↑ Bohn, Dieter (19 May 2021). "iPad Pro (2021) review: the best screen, but is that enough?". The Verge. Retrieved 17 February 2024.
  41. ↑ "TFT Central". Archived from the original on 15 October 2016. Retrieved 13 November 2016.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.