Lysdiode-bagbelyst LCD-skærm

Lay repair of diodes used to illuminate the display at the television. It may look barbaric, but 4 times the TV was fixed so much that the backlight was almost like new.

En lysdiode bagbelyst LCD-skærm er f.eks. et fjernsyn- eller computer-skærm som i stedet for koldkatode lysstofrør (eng. CCFL) benytter lysdioder til bagbelysning. ^[1] Lysdiodeenheden som belyser LCD-skærmen kaldes en LED-BLU (LED-BackLighting Unit).

Indenfor tv-branchen kaldes et TV med lysdiode bagbelyst LCD-skærm for LED-TV (termen benyttes af Samsung Electronics, Toshiba, Philips, LG Electronics og Vizio).

Lysdioder i deres nuværende form er alt for store til at være individuelle pixels på traditionelle fjernsyn. Anvendelsen af en ægte lysdiodeskærm er derfor reserveret til meget større skærme på sportspladser og andre kommercielle steder.

Lysdiodebagbelysningen kan komme i flere former:

Hvide lysdioder spredt langs kanten – Edge-LED – er den mest udbredte form da den er billigst og kan skabe meget tynde Tv-modeller. Et specielt diffusionspanel anvendes til at sprede lyset jævnt bag skærmen^[2]. Ulempen ved Edge-LED kan imidlertid være, at baggrundslyset fordeles inhomogent over LCD panelet^[3].
Hvide lysdioder spredt bag skærmen – Direct-LED – evt. kan lysdioderne lokalt dæmpes i takt med ønsket lokal max. lys niveau. Fordelen er at kontrasten bliver meget større og energiforbruget lavere.
Røde, grønne og blå lysdioder sat sammen og spredt bag skærmen – Dynamic RGB LED (RGB-farver) – evt. kan lysdioderne lokalt dæmpes i takt med ønsket lokal max. lys niveau. Fordelen er at kontrasten bliver meget større og energiforbruget lavere.

Lysdiodebagbelysning sammenlignet med traditionel koldkatode lysstofrør

Lysdiode bagbelyst LCD-skærm adskiller sig væsentligt fra konventionelle LCD-skærme med koldkatode lysstofrør på flere vigtige områder^[4]:

De kan fremvise et billede med større dynamisk kontrast.
Med Edge-LED-bagbelysning kan de laves yderst tynde. Aktuelle modeller er kun lidt tykkere end 25mm.
De bruger mindre energi – især efter kalibrering. Min. 10%^[5] og i snit omkring 40% mindre end koldkatode lysstofrør.
Potentielt længere levetid.^[6]^[7]
Mindre farvefalmen igennem levetiden.^[7]
De kan formidle en større farve gamut, specielt når RGB-LED bagbelysning benyttes.^[8]
Mindre miljøforurening når de sendes til affaldspladsen.
Dyrere i det aktuelle marked.
Kan give mindre EMI^[9], hvilket kan betyde færre udgifter til filtreringskredsløb.

Kilder/referencer

^ What's an LED TV?, New York Times Gadgetwise Blog, 11-JUN-2009
^ Hvad er LED TV?
^ Samsung B8050 test – inhomogen baggrundsbelysning/clouding
^ "ledtele.co.uk: LED vs LCD Comparison Guide". Arkiveret fra originalen 15. oktober 2009. Hentet 1. november 2009.
^ April 26, 2006, infoworld.com: LED technology makes flat-panel displays brighter. New backlighting technology creates more vibrant colors and sharper images for users Citat: "... LED backlights reduce power usage by at least 10 percent compared to older technologies, Liu said. ..."
^ flatpanels.dk: Monitor Teknologi – Uddybende information om monitor teknologi Arkiveret 25. oktober 2009 hos Wayback Machine Citat: "...Med LEDs...længere levetid – helt op til 100.000 og 1.000.000 timer, hvor man med fluorescerende lamper typisk har en levetid på mellem 50.000-60.000 timer..."
^ ^a ^b Jun 6th 2007, engadget.com: MacBook Pro backlight comparison: LED vs CCFL Citat: "...Yes, we're aware CCFL displays eventually wear down and lose their brightness, but either there really is a huge difference in CCFL and LED, or the 8-month old MBP we tested against in the photos had really worn down. Our suspicion is that it's a bit of both...Reader Comment...The 15" LED MacBook Pros extends battery life 30-60 minutes when compared to the older MacBook Pros. This includes battery savings from the LED itself as well as the new Santa Rosa chipset..."
^ September 05, 2008, audioholics.com: Flat Panel Trends – Thin is In and Speed Kills Citat: "...Some trends we observed overall: LED-based LCD panels looked, to us, just as black as the best plasma displays we've seen...Let me make this implicitly clear: LCD displays running with Triluminos RGB LED backlights are just as good as any plasma display I've seen to-date...The differences between LED backlit and florescent backlit displays is amazing..."
^ 2007, CI Lumen Enhances LCD Brightness with Low-Power LED Backlighting Citat: "...Because LEDs do not require an inverter, EMI emissions can be reduced. Additionally, no heater is needed as with CCFLs so LEDs can be turned on to full brightness immediately..."

Se også

Laser-tv

[1] What's an LED TV?, New York Times Gadgetwise Blog, 11-JUN-2009

[2] Hvad er LED TV?

[3] Samsung B8050 test – inhomogen baggrundsbelysning/clouding

[4] "ledtele.co.uk: LED vs LCD Comparison Guide". Arkiveret fra originalen 15. oktober 2009. Hentet 1. november 2009.

[5] April 26, 2006, infoworld.com: LED technology makes flat-panel displays brighter. New backlighting technology creates more vibrant colors and sharper images for users Citat: "... LED backlights reduce power usage by at least 10 percent compared to older technologies, Liu said. ..."

[6] tpanels.dk: Monitor Teknologi – Uddybende information om monitor teknologi Arkiveret 25. oktober 2009 hos Wayback Machine Citat: "...Med LEDs...længere levetid – helt op til 100.000 og 1.000.000 timer, hvor man med fluorescerende lamper typisk har en levetid på mellem 50.000-60.000 timer..."

[macbook-7] Jun 6th 2007, engadget.com: MacBook Pro backlight comparison: LED vs CCFL Citat: "...Yes, we're aware CCFL displays eventually wear down and lose their brightness, but either there really is a huge difference in CCFL and LED, or the 8-month old MBP we tested against in the photos had really worn down. Our suspicion is that it's a bit of both...Reader Comment...The 15" LED MacBook Pros extends battery life 30-60 minutes when compared to the older MacBook Pros. This includes battery savings from the LED itself as well as the new Santa Rosa chipset..."

[8] September 05, 2008, audioholics.com: Flat Panel Trends – Thin is In and Speed Kills Citat: "...Some trends we observed overall: LED-based LCD panels looked, to us, just as black as the best plasma displays we've seen...Let me make this implicitly clear: LCD displays running with Triluminos RGB LED backlights are just as good as any plasma display I've seen to-date...The differences between LED backlit and florescent backlit displays is amazing..."

[9] 2007, CI Lumen Enhances LCD Brightness with Low-Power LED Backlighting Citat: "...Because LEDs do not require an inverter, EMI emissions can be reduced. Additionally, no heater is needed as with CCFLs so LEDs can be turned on to full brightness immediately..."

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