As known, TV forms an image using an OLED or LCD panel. OLED uses self-lit LEDs and does not require backlit, which provides superb picture quality at the expense of huge contrast due to perfect deep blacks. But its price rises sharply with the increase in screen size, which significantly limits their popularity. In addition, they are limited in brightness, which reduces their HDR performance.
LCD TVs are significantly cheaper and brighter, but their contrast and, therefore, picture quality is significantly lower. However, Quantum Dot technology and Local Dimming, especially with the innovative mini LED backlit, have significantly expanded their color gamut, color accuracy, brightness and contrast. As a result, LCD TVs with QD display and mini LED backlit today provide superb picture quality. But, of course, apart from these technologies, the image quality depends on the panel.
As known, the LCD TV creates a color image using subpixels of red, green and blue, which are actually color filters for dyeing white light.
LCD panel works as follows. Backlit illuminates pixels evenly. When the intensity is the same, the red, green and blue subpixels are mixed to form white. But the generation of shades requires light blocking control for each subpixel.
LCD panel solves this problem with vertical and horizontal polarizing filters. First, the vertical filter “flips” the light into a vertical plane, it becomes polarized in one plane and can no pass through the horizontal filter.
As known, the light transmission of crystals depends on their polarization. Accordingly, an array of liquid crystals between the two polarizing filters regulates the light intensity by changing the polarization of the crystals under the influence of current.
In fact, liquid crystals control the light by adjusting its intensity. This technology is implemented in several ways.
TN & IPS panels
The cheapest TN (twisted nematic crystal) matrix uses liquid crystals that are twisted into a spiral. It transmits 100% of the light in a twisted state and blocks out light in a chaotic state.
Unfortunately, TN matrices can only transmit 6 bits per channel, i.e. 262 144 shades of color (two in sixth degree for red, green and blue). In addition, they have a very narrow vertical viewing angle. These factors have actually supplanted TN-panels from modern TVs.
Crystals in the IPS (In-Plane Switching) panel are always oriented in one direction. At the same time, by default, they are oriented horizontally and completely block the light.
Unlike TN, IPS can adjust the rotation angle of the crystal, changing the amount of light transmitted and smoothly adjusting the brightness of each pixel.
They are easy to calibrate and can transmit up to 10 bits per channel or 1.07 billion shades. In addition, more efficient light scattering dramatically increases the viewing angle.
A macro photograph of the IPS-panel structure demonstrates the relative position of its pixels.
Unfortunately, the first IPS panels had high response times of up to 50ms. But modern expensive panels provide about 4ms. Secondly, a sufficiently large distance between the crystals does not effectively block the backlit, deteriorating the black depth and, accordingly, the contrast.
Unfortunately, companies often do not indicate the panel type. But the user can easily determine this on his own. First, when viewed from the side, the image on the VA panel fades significantly more.
In addition, the VA panel retains the plume of pixels even with light mechanical impact on the screen surface.
Crystals in a VA (Vertical Alignment) panel are located in a vertical plane perpendicular to the polarizing filters.
This arrangement significantly improves backlit blocking, providing a 3-5x contrast improvement. The native contrast of VA panels is 6,000: 1 vs 1,400: 1 for IPS. Modern VA panels provide black depths from 0.015 to 0.025 nits, IPS – from 0.075 to 0.090 nits.
Unfortunately, VA does not provide a stepless adjustment of the crystal angle, excluding the possibility of stepless adjustment of the brightness for each subpixel. Therefore, VA color accuracy is significantly worse compared to IPS.
But the multi-domain structure of modern VA-matrix uses multiple liquid crystal units with separate control for each sub-pixel, providing several levels of their brightness. Therefore, modern VA panels support 8-bit color. Moreover, FRC (Frame Rate Control) technology with fast flashing of the pixel increases it to almost 10-bit image by quasi-interpolation of colors.
In addition, the technologies differ in terms of backlit. As known, today Local Dimming technology in LCD TVs most effectively increases their contrast and expands the dynamic range by turning off the backlit in the dark areas of the frame.
In turn, these specs directly affect the performance of the popular HDR mode. But FALD (Full Array Local Dimming) works most effectively with VA panels and less pronounced in IPS panels. Therefore, IPS panels often use Edge-LED backlit, which illuminates the screen by scattering light from the side LEDs using a diffuse filter. But it’s less uniform and does not support Local Dimming. Therefore, modern premium LCD TVs are more to use VA panels with FALD.
The color gamut of both technologies depends on the panel bitness. Accordingly, 10-bit 4K VA and IPS panels deliver 1,070,000,000 shades.
In addition, companies are developing new technologies. For example, the Chinese BOE Technology (Beijing Orient Electronics Group) has been successfully developing a very promising ADSDS (Advanced Super Dimension Switch) technology for several years, which is an improved IPS version. Teaming up with Korea’s HYDIS (Hyundai Display), it has been developing and manufacturing TFT, LCD and OLED panels since 2003. Today this technology is also known as ADS or ADS-FFS (Fringe Field Switching) or IPS-ADS, and is used in devices from Samsung, LG, Xiaomi, Huawei, TCL, Apple, etc.
Like IPS, ADSDS uses a perpendicular crystal arrangement in relation to the luminous flux, but additionally uses Plane-to-Line Switiching technology to optimize crystal offset.
Unlike IPS, its structure uses longitudinal and transverse electric fields for the parallel movement of liquid crystals.
In addition, the ADS uses the luminous flux more efficiently due to the used indium tin oxide. This material is very durable and reliable, improves color rendering, increases viewing angles, and has a very high light transmittance, increasing the screen brightness. In addition, its 100% transparency allowed developers to place controls on top of the crystalline film. The lack of additional protective coating increases the viewing angles by several degrees.
ADS panels are often used in TVs today, but they are especially popular in portable devices due to their low power consumption.
Thanks to the efforts of development companies and industry leaders, including Sony, Panasonic, LG, Samsung, TCL, the list of panels is constantly expanding and today it includes S-IPS, H-IPS, P-IPS, IPS-Pro, MVA, PVA, ADSDS, etc. Of course, each modification has its own pros & cons. For example, the Nano IPS panels with low Input lag work successfully even in gaming monitors.
Modern LG LCD TVs mainly use IPS panels, while Samsung uses VA panels. The competition between these giants has been going on for many years. This year, the companies presented a series with the innovative mini LED backlit. As a result, the competition between Samsung Neo QLED mini LED vs LG OLED mini LED, and Samsung Neo QLED vs LG QNED has already started. Of course, the outcome of their rivalry will depend on many factors, including the effectiveness of Local Dimming algorithms, HDR performance, etc. But the panel type will also matter.
This video offers a side-by-side comparison of LG IPS TV with FALD (full array local dimming) vs Samsung VA TV with Edge LED.