Although LED is similar in spelling to OLED, it refers to a completely different technology. A liquid crystal LED TV, what does it mean, is a device using a different backlight system compared to conventional lcd models. And if OLED (Organic Light-Emitting Diode) means that the screen consists of organic light-emitting diodes, then LED (Light Emitting Diode) is the use of diodes to illuminate the matrix of a liquid crystal television receiver.
LED (Light Emitting Diode) - a light emitting diode, and in television technology, this abbreviation means liquid crystal matrix (LCD) screen and backlit by these light emitting diodes. After the introduction of a new type of backlight, TV manufacturers in the names of models began to replace "LCD" with "LED".
This was done more from a marketing point of view. In fact, it was not a new screen technology, but only a different kind of backlight. But this name of TVs has been preserved and is used today.
If ordinary LCD TVs use a cold cathode lamp, the same fluorescent (fluorescent) lamps (Cold Cathode Fluorescent Lamps, CCFL), then lcd led use light emitting diodes. As you know, LCD (lcd) screens in TVs consist of cells (pixels) with liquid crystals and, depending on the position of the crystal in the cell, transmits light or not. This is how the screen glows.
The quality of the LCD matrix affects such parameters as static contrast, black level, viewing angles, refresh rate, response time. There are such technologies for the production of a matrix on liquid crystals for TVs: TN, IPS (S-IPS, IPS-Pro, P-IPS, AH-IPS), VA / MVA / PVA, PLS.
Parameters such as brightness, color rendering, color gamut, dynamic contrast depend on the backlight. Although it is more correct to consider the matrix + backlight system on the TV and measure the parameters for it.
Manufacturers claim that the use of LED backlighting can increase:
- brightness,
- contrast,
- image clarity,
- color range.
The power consumption of an LED TV is also reduced by about 40%. Also, ice TVs do not use mercury, which is used in fluorescent lamps, which affects the environment.
Indeed, modern ultra-bright LEDs can provide a high brightness of the image on the display.
The contrast is increased and the concept of dynamic contrast is introduced, when the brightness of the LEDs is adjusted locally for different parts of the screen, and due to this, the dynamic contrast indicator increases. At the same time, the level of static contrast of the TV remains the same, it depends on the display matrix.
The black level is also improved by adjusting the glow of the diodes while watching a video. In a dark scene, the backlight level is reduced and the screen becomes darker, and hence the black level improves.
But as for increasing the color gamut of the TV, here you need to consider everything in more detail.
White or composite LEDs
Technologically, the backlight of the display in the LCD TV is carried out from LEDs. To do this, white diodes are used, the light from which enters the filters and get blue, green and red colors. This type is called WLED.
To improve the color gamut, they first began to use three types of LEDs as backlight at once: red, green, blue. This technology is called RGB LED.
But it was not possible to obtain the required spectrum of light with the help of such technologies. And the color gamut was not enough for use in UHD TVs. To solve this problem, new types of LEDs in TVs were invented.
Now premium TV models use composite diodes (GB-R LED, RB-G LED) or quantum dots.
Composite LEDs combine blue and green into one and coat with red phosphor (GB-R), or alternatively combine red and blue and coat with green phosphor (RB-G).
Quantum dots in LED TV
A completely different technology for changing the WLED backlight was proposed by Nanosys.
Quantum dots in the TV replace part of the diodes, in this case red and green. Only the blue LED remains, which generates a stream of light both to excite the quantum dots and to operate the blue sub-pixels on the screen. And the flow of light to the red and green sub-pixels form quantum dots.
Ice backlight methods
To improve the quality of the image on the TV screen, local dimming technology appeared, according to which the LEDs are controlled by groups of several diodes. The local dimming system has several drawbacks:
- 1) poor color uniformity in the image, that is, bright and dark spots are noticeable in areas where the backlight is brightly turned on and off;
- 2) colored halos appear on contrasting transitions;
- 3) image details disappear in dark areas.
These shortcomings are difficult to determine from a normal video picture on a TV screen, so today the local dimming method is widely used in models with led backlighting.
You can also divide LED TVs by the way the LEDs are arranged: Direct and Edge.
Direct - this is when the diodes are located evenly behind the screen, in the form of a matrix.
Edge is when they are located around the perimeter of the screen together with a diffuser panel. With such an arrangement, it is impossible to make effective local dimming using the local dimming method.
With the Direct method, you can get a more uniform backlight than with the Edge method, but the thickness of the TV and power consumption will increase due to the increase in the number of LEDs. Ultra-thin TVs (thickness can be less than 3 centimeters) can only be obtained by applying the Edge diode arrangement.
Due to its efficiency and at the same time showing fairly good results, the most commonly used side (Edge) backlight with local dimming.
For 2015, LED TVs won the competition from plasma TVs, and OLED panels still cannot be compared with ice models in terms of cost. Therefore, in 2015, all the world's manufacturers in the model range of TVs all the places are occupied by LED devices. Only a few manufacturers have dared to release OLED TVs, especially LG holds the lead here. So when buying a TV this year, you will definitely buy the LED model.
