Editing Liquid-crystal display (section)

==Illumination==
{{Main|Backlight}}
[[File:Medical Econet PalmCare - display module - LED-backlit LCD-1405.jpg|thumb|An LED backlight for a handheld LCD device]]
LCDs do not produce light on their own, so they require external light to produce a visible image.<ref>{{Cite book|last=OECD|url=https://books.google.com/books?id=WgubAwAAQBAJ&q=Since+LCDs+produce+no+light+of+their+own,+they+require+external+light+to+produce+a+visible+image&pg=PA195|title=Information Technology Outlook 2000 ICTs, E-commerce and the Information Economy: ICTs, E-commerce and the Information Economy|date=March 7, 2000|publisher=OECD Publishing|isbn=978-92-64-18103-8 }}</ref><ref>{{Cite book|last=Ibrahim|first=Dogan|url=https://books.google.com/books?id=d0cvyIuJnL8C&q=Since+LCDs+produce+no+light+of+their+own,+they+require+external+light+to+produce+a+visible+image&pg=PP32|title=Using LEDs, LCDs and GLCDs in Microcontroller Projects|date=August 22, 2012|publisher=John Wiley & Sons|isbn=978-1-118-36103-0 }}</ref> In a transmissive type of LCD, the light source is provided at the back of the glass stack and is called a [[backlight]]. Active-matrix LCDs are almost always backlit.<ref>Explanation of different LCD monitor technologies, [http://reviews.cnet.com/monitor-buying-guide/ "Monitor buying guide&nbsp;— CNET Reviews"] {{Webarchive|url=https://web.archive.org/web/20140315183345/http://reviews.cnet.com/monitor-buying-guide/ |date=March 15, 2014 }}, Eric Franklin, Retrieved September 2012.</ref><ref>Explanation of different LCD monitor backlight technologies, [http://www.tftcentral.co.uk/articles/led_backlighting.htm "Monitor LED Backlighting"] {{Webarchive|url=https://web.archive.org/web/20210509072115/https://www.tftcentral.co.uk/articles/led_backlighting.htm |date=May 9, 2021 }}, TFT Central. Retrieved September 2012.</ref> Passive LCDs may be backlit but many are reflective as they use a reflective surface or film at the back of the glass stack to utilize ambient light. [[Transflective liquid-crystal display|Transflective LCDs]] combine the features of a backlit transmissive display and a reflective display.

The common implementations of LCD backlight technology are:
[[File:LCD-TV Backlight with CCFL.jpg|thumb|18 parallel CCFLs as backlight for a 42-inch (106 cm) LCD TV]]

* WLED array: The LCD panel is lit by a full array of white LEDs placed behind a diffuser behind the panel. LCDs that use this implementation will usually have the ability to dim or completely turn off the LEDs in the dark areas of the image being displayed, effectively increasing the contrast ratio of the display. The precision with which this can be done will depend on the number of dimming zones of the display. The more dimming zones, the more precise the dimming, with less obvious blooming artifacts which are visible as dark grey patches surrounded by the unlit areas of the LCD. As of 2012, this design gets most of its use from upscale, larger-screen LCD televisions.
* CCFL: The LCD panel is lit either by two [[Fluorescent lamp#Cold-cathode fluorescent lamps|cold cathode fluorescent lamps]] placed at opposite edges of the display or an array of parallel CCFLs behind larger displays. A diffuser (made of PMMA acrylic plastic, also known as a wave or light guide/guiding plate<ref name="auto">{{Cite web|url=https://www.oled-a.org/lcd-tvs-change-light-guide-plate-material-to-enable-thinner-tv-november13-2017.html |title=LCD TVs Change Light Guide Plate Material to Enable Thinner TV |date = November 13, 2017 |website= OLED Association|access-date=September 24, 2020|archive-date=November 26, 2020|archive-url=https://web.archive.org/web/20201126033112/https://www.oled-a.org/lcd-tvs-change-light-guide-plate-material-to-enable-thinner-tv-november13-2017.html |url-status=live}}</ref><ref>{{Cite web|url=https://patents.google.com/patent/US7142768B2/en |title=LCD optical waveguide device|access-date=September 24, 2020|archive-date=March 19, 2022|archive-url=https://web.archive.org/web/20220319080655/https://patents.google.com/patent/US7142768B2/en |url-status=live}}</ref>) then spreads the light out evenly across the whole display. For many years, this technology had been used almost exclusively. Unlike white LEDs, most CCFLs have an even-white spectral output resulting in better color gamut for the display. However, CCFLs are less energy efficient than LEDs and require a somewhat costly [[Inverter (electrical)|inverter]] to convert whatever DC voltage the device uses (usually 5 or 12&nbsp;V) to ≈1000 V needed to light a CCFL.<ref>Explanation of CCFL backlighting details, [http://www.designnews.com/document.asp?doc_id=212678 "Design News&nbsp;— Features&nbsp;— How to Backlight an LCD"] {{webarchive|url=https://web.archive.org/web/20140102192342/http://www.designnews.com/document.asp?doc_id=212678 |date=January 2, 2014}}, Randy Frank, Retrieved January 2013.</ref> The thickness of the inverter transformers also limits how thin the display can be made.
* EL-WLED: The LCD panel is lit by a row of white LEDs placed at one or more edges of the screen. A light diffuser (light guide plate, LGP) is then used to spread the light evenly across the whole display, similarly to edge-lit CCFL LCD backlights. The diffuser is made out of either PMMA plastic or special glass, PMMA is used in most cases because it is rugged, while special glass is used when the thickness of the LCD is of primary concern, because it doesn't expand as much when heated or exposed to moisture, which allows LCDs to be just 5mm thick. Quantum dots may be placed on top of the diffuser as a quantum dot enhancement film (QDEF, in which case they need a layer to be protected from heat and humidity) or on the color filter of the LCD, replacing the resists that are normally used.<ref name="auto" /> {{As of|2012|post=,}} this design is the most popular one in desktop computer monitors. It allows for the thinnest displays. Some LCD monitors using this technology have a feature called dynamic contrast, invented by Philips researchers Douglas Stanton, Martinus Stroomer and Adrianus de Vaan<ref name="USRE42428E">{{cite patent |title=Method of and device for generating an image having a desired brightness |invent1=D.A. Stanton |invent2=M.V.C. Stroomer |invent3=A.J.S.M. de Vaan |country=US |status=patent |number=RE42428E |pubdate=June 7, 2011}}</ref> 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<ref>{{cite web|title = Dimming options for LCD brightness |first = J. |last =Moronski|website = Electronicproducts.com|date = January 3, 2004|archive-date=July 28, 2017|archive-url=https://web.archive.org/web/20170728120219/http://www.electronicproducts.com/Optoelectronics/Dimming_options_for_LCD_brightness_control.aspx |url=http://www.electronicproducts.com/Optoelectronics/Dimming_options_for_LCD_brightness_control.aspx }}</ref>), the backlight is dimmed to the brightest color that appears on the screen while simultaneously boosting the LCD contrast to the maximum achievable levels, allowing the 1000:1 contrast ratio of the LCD panel to be scaled to different light intensities, resulting in the "30000:1" contrast ratios seen in the advertising on some of these monitors. Since computer screen images usually have full white somewhere in the image, the backlight will usually be at full intensity, making this "feature" mostly a marketing gimmick for computer monitors, however for TV screens it drastically increases the perceived contrast ratio and dynamic range, improves the viewing angle dependency and drastically reducing the power consumption of conventional LCD televisions.
* RGB-LED array: Similar to the WLED array, except the panel is lit by an array of [[RGB LED]]s.<ref>{{cite web | url=https://www.photonics.com/Articles/The_Road_Leads_Up_for_the_LED_Backlight_Unit/a35253 | title=The Road Leads up for the LED Backlight Unit Market }}</ref><ref>{{cite web | url=https://www.soundandvision.com/content/sony-kdl-55xbr8-lcd-tv | title=Sony KDL-55XBR8 LCD TV | date=November 19, 2008 }}</ref><ref>{{cite web |author-first1=Pierre|author-last1=de Greef|author-first2=Hendriek|author-last2=Groot Hulze|website=EE Times|publisher=AspenCore|url=https://www.eetimes.com/adaptive-dimming-and-adaptive-boosting-backlight-technologies-for-lcd-tv-systems/ | title=Adaptive dimming and adaptive boosting backlight technologies for LCD-TV systems | date=November 14, 2007 }}</ref><ref>{{cite web | url=https://www.trustedreviews.com/reviews/nec-spectraview-reference-21-lcd2180wg-led | title=NEC SpectraView Reference 21 (LCD2180WG LED) | date=November 18, 2005 }}</ref> While displays lit with white LEDs usually have a poorer color gamut than CCFL lit displays, panels lit with RGB LEDs have very wide color gamuts. This implementation is most popular on professional graphics editing LCDs. As of 2012, LCDs in this category usually cost more than $1000. As of 2016 the cost of this category has drastically reduced and such LCD televisions obtained same price levels as the former 28" (71&nbsp;cm) CRT based categories.
* Monochrome LEDs: such as red, green, yellow or blue LEDs are used in the small passive monochrome LCDs typically used in clocks, watches and small appliances. Blue LEDs can be used in LCDs with quantum dot enhancement film or quantum dot color filters.<ref>{{cite web | url=https://displaydaily.com/quantum-dot-display-technology-coming-to-lcd-s-rescue/ | title=Quantum Dot Display Technology Coming to LCD's Rescue | date=November 20, 2017 }}</ref><ref>{{cite web | url=https://spectrum.ieee.org/amp/your-guide-to-televisions-quantumdot-future-2650276702 | title=Your Guide to Television's Quantum-Dot Future }}</ref>
* Mini-LED: Backlighting with Mini-LEDs can support over a thousand Full-area Local Area Dimming (FLAD) zones. This allows deeper blacks and higher contrast ratio.<ref>{{Cite web|url=https://www.displayninja.com/mini-led-vs-microled/|title=Mini-LED vs MicroLED - What Is The Difference? [Simple Explanation]|last=Shafer|first=Rob|date=June 5, 2019|website=DisplayNinja |access-date=September 14, 2019|archive-date=April 5, 2021|archive-url=https://web.archive.org/web/20210405141647/https://www.displayninja.com/mini-led-vs-microled/|url-status=live}}</ref>

Today, most LCD screens are being designed with an [[LED-backlit LCD|LED backlight]] instead of the traditional CCFL backlight, while that backlight is dynamically controlled with the video information (dynamic backlight control). The combination with the dynamic backlight control, invented by Philips researchers Douglas Stanton, Martinus Stroomer and Adrianus de Vaan, simultaneously increases the dynamic range of the display system (also marketed as ''HDR'', ''high dynamic range television'' or ''FLAD'', ''full-area local area dimming'').<ref>{{cite web|title = LED local dimming explained|first =G. |last =Morrison|website = CNET.com/news|date = March 26, 2016|url = https://www.cnet.com/news/led-local-dimming-explained/ |archive-url=https://web.archive.org/web/20171123124120/https://www.cnet.com/news/led-local-dimming-explained/ |archive-date=November 23, 2017 }}</ref><ref>"[https://www.osapublishing.org/oe/viewmedia.cfm?uri=oe-25-3-1973&seq=0 Pixel-by-pixel local dimming for high dynamic range liquid crystal displays]"; H. Chen; R. Zhu; M.C. Li; S.L. Lee and S.T. Wu; Vol. 25, No. 3; February 6, 2017; Optics Express 1973</ref><ref name= "USRE42428E" />

The LCD backlight systems are made highly efficient by applying optical films such as prismatic structure (prism sheet) to gain the light into the desired viewer directions and reflective polarizing films that recycle the polarized light that was formerly absorbed by the first polarizer of the LCD (invented by Philips researchers Adrianus de Vaan and Paulus Schaareman),<ref>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# {{Webarchive|url=https://web.archive.org/web/20200724100633/https://worldwide.espacenet.com/publicationDetails/biblio?CC=EP&NR=0606939B1&KC=B1&FT=D&ND=5&date=19980506&DB=EPODOC&locale=en_EP |date=July 24, 2020 }}</ref> generally achieved using so called DBEF films manufactured and supplied by 3M.<ref>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 {{Webarchive|url=https://web.archive.org/web/20170802000049/http://multimedia.3m.com/mws/media/977332O/display-materials-systems-strategies-for-large-displays.pdf |date=August 2, 2017 }}</ref> Improved versions of the prism sheet have a wavy rather than a prismatic structure, and introduce waves laterally into the structure of the sheet while also varying the height of the waves, directing even more light towards the screen and reducing aliasing or moiré between the structure of the prism sheet and the subpixels of the LCD. A wavy structure is easier to mass-produce than a prismatic one using conventional diamond machine tools, which are used to make the rollers used to imprint the wavy structure into plastic sheets, thus producing prism sheets.<ref>{{Cite web|url=https://patents.google.com/patent/US8599504B2/en|title=Prism sheet having prisms with wave pattern, black light unit including the prism sheet, and liquid crystal display device including the black light unit|access-date=September 3, 2020|archive-date=March 19, 2022|archive-url=https://web.archive.org/web/20220319080656/https://patents.google.com/patent/US8599504B2/en|url-status=live}}</ref> A diffuser sheet is placed on both sides of the prism sheet to distribute the light of the backlight uniformly, while a mirror is placed behind the light guide plate to direct all light forwards. The prism sheet with its diffuser sheets are placed on top of the light guide plate.<ref>{{Cite web|url=https://www.laserfocusworld.com/optics/article/16552684/flatpanel-displays-wavy-prism-sheet-makes-lcds-look-better|title=StackPath|website=LaserFocusWorld.com|date=September 2007 |access-date=September 3, 2020|archive-date=November 26, 2020|archive-url=https://web.archive.org/web/20201126123809/https://www.laserfocusworld.com/optics/article/16552684/flatpanel-displays-wavy-prism-sheet-makes-lcds-look-better|url-status=live}}</ref><ref name="auto" /> The DBEF polarizers consist of a large stack of uniaxial oriented birefringent films that reflect the former absorbed polarization mode of the light.<ref>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; July 24, 2017; Optics Express 17499; https://www.osapublishing.org/oe/viewmedia.cfm?uri=oe-25-15-17499&seq=0</ref>

DBEF polarizers 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.<ref>Polarisation-sensitive beam splitter; D.J. Broer; A.J.S.M. de Vaan; J. Brambring; European patent EP0428213B1; July 27, 1994; https://worldwide.espacenet.com/publicationDetails/biblio?CC=EP&NR=0428213B1&KC=B1&FT=D# {{Webarchive|url=https://web.archive.org/web/20210308185634/https://worldwide.espacenet.com/publicationDetails/biblio?CC=EP&NR=0428213B1&KC=B1&FT=D |date=March 8, 2021 }}</ref> The combination of such reflective polarizers, and LED dynamic backlight control<ref name="USRE42428E" /> make today's LCD televisions far more efficient than the CRT-based sets, leading to a worldwide energy saving of 600 TWh (2017), equal to 10% of the electricity consumption of all households worldwide or equal to 2 times the energy production of all solar cells in the world.<ref>Energy Efficiency Success Story: TV Energy Consumption Shrinks as Screen Size and Performance Grow, Finds New CTA Study; Consumer Technology Association; press release July 12, 2017; https://cta.tech/News/Press-Releases/2017/July/Energy-Efficiency-Success-Story-TV-Energy-Consump.aspx {{Webarchive|url=https://web.archive.org/web/20171104120903/https://cta.tech/News/Press-Releases/2017/July/Energy-Efficiency-Success-Story-TV-Energy-Consump.aspx |date=November 4, 2017}}</ref><ref>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 {{Webarchive|url=https://web.archive.org/web/20170801234723/http://www.cta.tech/cta/media/policyImages/policyPDFs/Fraunhofer-LCD-TV-Power-Draw-Trends-FINAL.pdf |date=August 1, 2017}}</ref>