LED-backlit LCD television
Encyclopedia
An LED-backlight LCD television is an LCD television, flat panel display
that uses LED
backlighting instead of the cold cathode
(CCFL) backlighting used in other LCD televisions. While not an LED display
, it is called "LED TV" by some manufacturers and suppliers. The use of LED backlighting allows a thinner panel, lower power consumption, better heat dissipation, a brighter display, and better contrast levels.
Three forms of LED may be used:
-backlit LCD displays, LED-backlit LCD TVs and computer displays:
(OLED), OEL or AMOLED display technologies. In the UK the Advertising Standards Authority
(ASA) has made it clear in correspondence that it does not object to the use of the term 'LED TV', but does require it to be clarified in any advertising. 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 arranged around the inside frame of the TV and a light diffusion panel to spread the light evenly behind the LCD panel.
The variations of LED backlighting offer different benefits. The first commercial LED backlit LCD TV was the Sony
Qualia
005 introduced in 2004, which used RGB LED arrays to produce a color gamut around twice that of a conventional CCFL LCD television, possible because red, green and blue LEDs have very sharp spectral peaks which, combined with the LCD panel filters, results in significantly less bleed-though to adjacent color channels. In this way the 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 selected Sony BRAVIA
LCD models, with the addition of 'local dimming' which enables excellent on-screen contrast through selectively turning off the LEDs behind dark parts of a picture frame.
LED backlighting employing so-called "white" LEDs produces a broader spectrum source feeding the individual LCD panel filters that is more similar to CCFL sources, and hence results in a more limited display gamut than RGB LEDs, but at lower cost.
Edge-LED lighting was first introduced by Sony
in September 2008 on the 40 inch BRAVIA KLV-40ZX1M (referred to as the ZX1 in Europe). Edge-LED lighting for LCD televisions allows thinner housings; the Sony BRAVIA KLV-40ZX1M is 1cm thick; others are also extremely thin. The 55" Samsung LED8000 Smart TV has a 0.2" (5mm) bezel.
LED-backlit LCD TVs are claimed to have longer life and better energy efficiency than plasma
and CCFL LCD TVs. Unlike CCFL backlights, LEDs use no mercury, an environmental pollutant, in their manufacture. However, other elements such as gallium
and arsenic
are used in the manufacture of the LED emitters themselves; there is some debate over whether they are a better long-term solution to the problem of TV disposal.
Because LEDs can be switched on and off faster than CCFL displays 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 complicated by Edge-LED lighting not allowing these outputs to be reproduced simultaneously on-screen.
In September 2009 Nanoco
Group announced that it has signed a joint development agreement with a major Japanese electronics company under which it will design and develop quantum dots for LED Backlights in LCD televisions. Quantum dots are valued for displays, because they emit light in very specific gaussian distributions. This can result in a display that more accurately renders colors in the visible spectrum
.
to the supply current, switching the backlight off and on faster than the eye can perceive. If the dimming pulse frequency is too low or the user is very sensitive to flicker, this may cause discomfort and eye-strain, similar to the flicker of CRT displays at lower refresh rate
s. This can be tested by a user simply by 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 object 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, though this gives worse image quality and increased power consumption.
Flat panel display
Flat panel displays encompass a growing number of electronic visual display technologies. They are far lighter and thinner than traditional television sets and video displays that use cathode ray tubes , and are usually less than thick...
that uses LED
LEd
LEd is a TeX/LaTeX editing software working under Microsoft Windows. It is a freeware product....
backlighting instead of the cold cathode
Cold cathode
A cold cathode is a cathode used within nixie tubes, gas discharge lamps, discharge tubes, and some types of vacuum tube which is not electrically heated by the circuit to which it is connected...
(CCFL) backlighting used in other LCD televisions. While not an LED display
LED display
An LED display is a flat panel display, which uses light-emitting diodes as a video display. An LED panel is a small display, or a component of a larger display. They are typically used outdoors in store signs and billboards, and in recent years have also become commonly used in destination signs...
, it is called "LED TV" by some manufacturers and suppliers. The use of LED backlighting allows a thinner panel, lower power consumption, better heat dissipation, a brighter display, and better contrast levels.
Three forms of LED may be used:
- White edge-LEDs around the rim of the screen, using a special diffusion panel to spread the light evenly behind the screen (the most usual form)
- Dynamic RGB LEDs behind the panel
- A full array of LEDs arranged behind the screen whose brightness cannot be controlled individually
Edge-LEDs
This method of back-lighting allows LED-backlit TVs to be extremely thin. The light is diffused uniformly across the screen by a special panel.RGB dynamic LEDs
This method of backlighting allows local dimming of specific areas of darkness on the screen. This can show truer blacks, whites and PRs at much higher dynamic contrast ratios, at the cost of less detail in small, bright objects on a dark background, such as star fields as well as shadow detail.Full-array LEDs
Many brands use LED backlighting technology, which can offer benefits over CCFL LCD TVs of reduced energy consumption, better contrast and brightness, greater colour range, more rapid response to changes in scene and more accurate image rendering.Differences between LED-backlit and CCFL-backlit LCD displays
Compared to CCFLCold cathode
A cold cathode is a cathode used within nixie tubes, gas discharge lamps, discharge tubes, and some types of vacuum tube which is not electrically heated by the circuit to which it is connected...
-backlit LCD displays, LED-backlit LCD TVs and computer displays:
- produce images with greater dynamic contrast;
- with edge-LED lighting can be extremely slim, some screens are about one inch (2.5cm) thick;
- offer a wider color gamut when RGB-LED backlighting is used;
- produce less environmental pollution on disposal;
- are more expensive;
- have typically 20 to 30% lower power consumption;
- are more reliable;
- can allow a wider dimming range.
Technology
LCD-based televisions, often described as 'LED TVs', are not self-illuminating Organic light-emitting diodeOrganic light-emitting diode
An OLED is a light-emitting diode in which the emissive electroluminescent layer is a film of organic compounds which emit light in response to an electric current. This layer of organic semiconductor material is situated between two electrodes...
(OLED), OEL or AMOLED display technologies. In the UK the Advertising Standards Authority
Advertising Standards Authority (United Kingdom)
The Advertising Standards Authority is the self-regulatory organisation of the advertising industry in the United Kingdom. The ASA is a non-statutory organisation and so cannot interpret or enforce legislation. However, its code of advertising practice broadly reflects legislation in many instances...
(ASA) has made it clear in correspondence that it does not object to the use of the term 'LED TV', but does require it to be clarified in any advertising. 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 arranged around the inside frame of the TV and a light diffusion panel to spread the light evenly behind the LCD panel.
The variations of LED backlighting offer different benefits. The first commercial LED backlit LCD TV was the Sony
Sony
, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....
Qualia
Qualia (Sony)
Qualia was a boutique brand of high-end electronics, created by Sony to showcase their best technology. Some Qualia products are brand new while others are upgraded and rebranded versions of regular Sony products. The line was launched in Japan in June 2003 and the U.S. in April 2004. In 2005, Sony...
005 introduced in 2004, which used RGB LED arrays to produce a color gamut around twice that of a conventional CCFL LCD television, possible because red, green and blue LEDs have very sharp spectral peaks which, combined with the LCD panel filters, results in significantly less bleed-though to adjacent color channels. In this way the 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 selected Sony BRAVIA
BRAVIA
BRAVIA is a Sony brand used to market its high-definition LCD televisions, projection TVs and front projectors and for the PlayStation 3 , along with its home cinema range under the sub-brand BRAVIA Theatre. The BRAVIA name is an acronym of "Best Resolution Audio Visual Integrated Architecture"...
LCD models, with the addition of 'local dimming' which enables excellent on-screen contrast through selectively turning off the LEDs behind dark parts of a picture frame.
LED backlighting employing so-called "white" LEDs produces a broader spectrum source feeding the individual LCD panel filters that is more similar to CCFL sources, and hence results in a more limited display gamut than RGB LEDs, but at lower cost.
Edge-LED lighting was first introduced by Sony
Sony
, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....
in September 2008 on the 40 inch BRAVIA KLV-40ZX1M (referred to as the ZX1 in Europe). Edge-LED lighting for LCD televisions allows thinner housings; the Sony BRAVIA KLV-40ZX1M is 1cm thick; others are also extremely thin. The 55" Samsung LED8000 Smart TV has a 0.2" (5mm) bezel.
LED-backlit LCD TVs are claimed to have longer life and better energy efficiency than plasma
Plasma display
A plasma display panel is a type of flat panel display common to large TV displays or larger. They are called "plasma" displays because the technology utilizes small cells containing electrically charged ionized gases, or what are in essence chambers more commonly known as fluorescent...
and CCFL LCD TVs. Unlike CCFL backlights, LEDs use no mercury, an environmental pollutant, in their manufacture. However, other elements such as gallium
Gallium
Gallium is a chemical element that has the symbol Ga and atomic number 31. Elemental gallium does not occur in nature, but as the gallium salt in trace amounts in bauxite and zinc ores. A soft silvery metallic poor metal, elemental gallium is a brittle solid at low temperatures. As it liquefies...
and arsenic
Arsenic
Arsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.Arsenic is a metalloid...
are used in the manufacture of the LED emitters themselves; there is some debate over whether they are a better long-term solution to the problem of TV disposal.
Because LEDs can be switched on and off faster than CCFL displays 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 complicated by Edge-LED lighting not allowing these outputs to be reproduced simultaneously on-screen.
In September 2009 Nanoco
Nanoco
Nanoco is a nanotechnology company located in Manchester, United Kingdom founded in 2001. The company is a spinoff of research pursued at the University of Manchester....
Group announced that it has signed a joint development agreement with a major Japanese electronics company under which it will design and develop quantum dots for LED Backlights in LCD televisions. Quantum dots are valued for displays, because they emit light in very specific gaussian distributions. This can result in a display that more accurately renders colors in the visible spectrum
Visible spectrum
The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A typical human eye will respond to wavelengths from about 390 to 750 nm. In terms of...
.
Flicker due to backlight dimming
LED backlights are often dimmed by applying pulse-width modulationPulse-width modulation
Pulse-width modulation , or pulse-duration modulation , is a commonly used technique for controlling power to inertial electrical devices, made practical by modern electronic power switches....
to the supply current, switching the backlight off and on faster than the eye can perceive. If the dimming pulse frequency is too low or the user is very sensitive to flicker, this may cause discomfort and eye-strain, similar to the flicker of CRT displays at lower refresh rate
Refresh rate
The refresh rate is the number of times in a second that a display hardware draws the data...
s. This can be tested by a user simply by 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 object 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, though this gives worse image quality and increased power consumption.