Introduction

A liquid crystal display using LED backlighting rather than typical cold cathode fluorescent (CCFL) backlighting is referred to as an LED-backlit LCD.  LED-backlit LCDs use the same TFT LCD (thin-film-transistor liquid-crystal display) technologies as CCFL-backlit LCDs, but they have a number of advantages. While not technically an LED display, several manufacturers and suppliers market a television with an LED backlight and an LCD panel as an LED TV.

LED assemblages

LED backlights use a few to several hundred white, RGB, or blue LEDs to replace CCFL (fluorescent) bulbs. There are four different sorts of LED arrangements that can be used.

Edge-lighting (ELED)

Around the screen’s rim, LEDs create a line.

Direct lighting (DLED)

LEDs are evenly distributed in an array right beneath the screen.

Fading on a local level

Individually controlled direct-light LED clusters (rectangles, rows, and columns).

Local fading across the entire array (FALD)

Individually regulated LEDs for direct lighting. To diffuse the light uniformly behind the screen, a special diffusion panel (light guiding plate, LGP) is sometimes utilized. Backlighting with the local dimming method allows you to dynamically control the level of light intensity in specific areas of darkness on the screen, resulting in much higher dynamic-contrast ratios at the cost of less detail in small, bright objects on a dark background, such as star fields or shadow details. According to a study published in January 2016 by the University of California (Berkeley), subjectively perceived visual improvement with common contrast source material peaks at around 60 LCD locals.

Technology

LCDs with LED backlighting are not self-illuminating (unlike pure-LED systems). Backlighting an LCD panel with LEDs can be done in a variety of ways, including employing white or RGB (Red, Green, and Blue) LED arrays behind the display, as well as 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). LED backlighting comes in a variety of shapes and sizes, each with its own set of advantages. The Sony Qualia 005 (launched in 2004) was the first commercial full-array LED-backlit LCD TV, using RGB LED arrays to offer a colour spectrum roughly twice that of a standard CCFL LCD television. This was made possible by the presence of red, green, and blue LEDs.

Quantum dot enhancement film is a film that uses quantum dots to enhance their appearance (QDEF)

Photo luminescent quantum dots are valuable in displays because they emit light in precise, limited normal wavelength distributions. To provide white light suitable for use as an LCD backlight, quantum dots turn sections of the light from a blue-emitting LED into small-bandwidth green and red light, resulting in a nearly perfect colour gamut created by the LCD panel’s RGB colour filters. Furthermore, efficiency is enhanced because intermediate colours are no longer present and do not need to be filtered out by the LCD screen’s colour filters. This may result in a display that represents colours in the visible spectrum more accurately.

Miniature LEDs

Mini LED displays are LED-backlit LCDs with Mini LED–based backlighting that can handle over a thousand FALD zones (full array local dimming). Deeper blacks and a greater contrast ratio are possible as a result of this. This is not to be confused with the term “micro LED.”

Flicker in the backlight dims

LED backlights are frequently muted by applying pulse-width modulation to the source current, which causes the backlight to turn on and off faster than the human eye can detect. If the dimming-pulse frequency is too low, or if the user is sensitive to flicker, discomfort and eyestrain may result (similar to the flicker of CRT displays at lower refresh rates).  A user can check this by moving their hand in front of the screen; if the edges are clearly defined as the hand moves, the backlight is flashing at a low frequency. The display has a continually lighted backlight or is functioning at a frequency that is too high to discern if the hand seems fuzzy. Flicker is a type of flicker.

Backlighting with RGB LEDs

The block diagram of an LCD TV power supply with RGB LED backlight design can be found in Figure 2. The LCD TV’s power supply includes a 12V signal-processing board, a 24V backlight-driving circuit, and a 5V standby-power supply. The backlight driving circuit is made up of three power converters, as illustrated in Figure 3. In RGB LED backlight modules, backlight LEDs are linked both in series and parallel. Brightness differences are caused by differences in LED current/voltage characteristics. As a result, for LED backlight applications, dimming control is a crucial design concern. For current regulation of parallel connected LED arrays, we looked into three dimming methods: transcontinental.

Figure 2: An LCD TV Power Supply is shown in block diagram form.

LED’s Ascension

Backlights made of LEDs (Light Emitting Diodes) are ‘interesting’ to consumers since they allow for a thinner, lighter, and more efficient display. Manufacturers are eager to make an artificial contrast between their ‘LED’ (backlit) monitors and their ‘LCD’ monitors, so it’s also a marketing winner. This leads people to believe that the technology was fundamentally different from ‘LCD,’ and not just a switch from CCFL (Cold Cathode Fluorescent Lamp) to LED backlighting. Manufacturers can also make better use of the ‘dynamic contrast’ function, which we frequently criticize in our assessments, because to the quick brightness adjustments. The ease with which you may modify the full illumination to suit your needs.

When compared to WCG (Wide Color Gamut) CCFL backlights, the fundamental disadvantage of older LED backlight technologies is the limited spectrum range of the light they emit. This was one of the main reasons why some manufacturers were hesitant to remove CCFL backlighting from some of their ‘professional’ models – it was almost entirely for the purpose of creating wider colour gamut’s, which are required for image processing and viewing extended colour gamut’s like Adobe RGB. Despite these possible problems, many manufacturers accepted the technology as a “standard,” mostly for environmental concerns and to meet the needs of the bulk of the market.

Conclusion

By using ‘triads’ of LEDs (red, green, and blue) to provide broad-spectrum white light, a relatively small number of LED-backlit displays really surpassed the colour gamut limitation (and then some). RGB-LED backlighting was an unusual alternative to WLED (White Light Emitting Diode, the common approach discussed below). Samsung’s XL20, XL24, and XL30 monitors and TVs are notable models. Samsung was one of the first manufacturers to widely deploy LED backlight technologies to both monitors and TVs. Despite the fact that RGB-LED designs had colour gamut’s that WCG-CCFL backlights couldn’t match, the technology never truly took off.