TVs. Part 1. Types of TVs, backlights and technologies, practical differences

Hello, dear habrasociety.

I hope this article can help those like me - those people who choose a TV, but do not really know the subtle technical issues in this area. I would like to share with you my thoughts and practical conclusions regarding the choice of a large and high-quality TV.
For the last 3 years I watched 42 "LCD CCFL (this is when the image is formed by polarized light from fluorescent lamps, passed through the filters). In 2009, there was no 3D yet, and thin TVs with LED-backlighting just appeared and cost dishonest money. It was bought without any particular torment of choice for $ 1400.
For a couple of years of contemplation, I realized that I was missing something in the image. What - I could not describe, because I did not possess the necessary knowledge in this area. I knew for sure that I wanted a larger diagonal and a deeper black.

After studying the materiel, I clarified some points.

I Type of imaging.

Today, there are 3 types of image formation on modern TVs:

1 LCD.
The most common type of TV. Images in such TVs are obtained using polarized light, several light filters and controlled liquid crystals.

1.1 Types of LCD TV backlights.
Since the image that we see on the LCD TV screen is obtained as a result of the passage of polarized light from the backlight, it is necessary to designate 2 types of backlight:
a) CCFL, which is also the cold cathode. A subspecies of thin fluorescent lamps located behind the matrix.
Advantages: uniform illumination.
Disadvantages: large thickness, power consumption, the inability to control the backlight locally.
b) LED - light emitting diodes. Currently, TVs with a cold cathode are almost completely replaced.
Advantages: it is possible to make very thin TVs, low power consumption, the ability to control the backlight locally.

A few words should be said about the local backlight control and the LED backlight division. LED backlighting is divided into 2 types: edge (it is EDGE-LED, when the LEDs are located at the edges of the matrix, their light hits the diffuser and is scattered) and carpet (Full HD LED, LED Pro). Since the LCD pixels themselves do not emit light, they need backlight (as mentioned above), which is always on. Closed crystals still transmit light, so it is impossible to achieve a low black level (the lower the better) and contrast transitions in systems with edge illumination. The highest-level televisions use carpet backlight (when the LEDs are located directly behind the matrix). This allows you to increase the uniformity of the backlight and introduce segmented backlight control when individual diodes, responsible for areas on the screen, can dim the brightness depending on the scene on the screen. In fact, only 2 series have carpet backlight - the 9th Philips series and the 9th Sony series. In the 9th series, LG also has carpet backlighting, but its implementation is worse than the edge in competitive solutions.

Uneven backlight.
Due to the fact that the LEDs are arranged at a certain frequency (scattering and many other factors contribute to it), in almost 100% of cases, LED-backlit LCD TVs have clouding - when areas that should remain black have a different gradation gray.
The problem is partially solved by segmented LED backlighting.

1.2 Types of matrix LCD-TVs with LED-backlight.
I will not go into the details of image formation by different types of matrices, but briefly describe their main advantages and disadvantages.
a) IPS (now only produces LG). Matrices, which, in my opinion, are ideal for low and medium level TVs.
Advantages: large viewing angles.
Disadvantages: high black level (~ 0.16 nits), long response time.
They are installed in LG TVs of 3–9 series (that is, practically in everything, without separation by level), Philips 4, 6 series, Panasonic of various variations and many others.
b) S-PVA (manufactured by Samsung). Matrixes for TVs of classes above.
Benefits:deeper black (0.05-0.1 nits depending on the implementation of the backlight).
They are installed in Samsung 7-8 series TVs, Sony 7-8 series, Philips 7-8 series and some others.
c) UV²A (manufactured by Sharp). In my opinion, the most advanced type of matrix.
Advantages: angles are greater than S-PVA (but smaller than IPS). The deepest black level (0.02 - 0.06 nits)
Disadvantages: Sharp produces them in insufficient quantities.
Installed on Philips 9 Series TVs and Sharp's top-end series.

2. Plasma.
There are a lot of myths and misconceptions associated with this word. Any ignorant seller will definitely tell you that the plasma is out of date. This is due to the set of stereotypes and problems that have taken place.
The image is formed using the glow of the phosphor under the influence of UV rays.
Each plasma cell is an independent light source, so the TV does not require backlight. Previously, plasma TVs had a very large thickness and cell size, so they were very bulky and the Full HD diagonals started from 50-60 ". Now the thickness of modern plasma TVs does not exceed 3-4 cm, and the diagonals start from 42".

Plasma televisions do not have various types of matrices with marketing names, but there are generations of panels (the most perfect is the 15th).

Now plasma is almost replaced by LCD-TVs and only 3 companies are engaged in its production: Panasonic, Samsung and LG (moreover, only the first 2 have their own developments). This is due to the loss of production, competition from LCD TVs and their popularization. But plasma holds the first positions in large diagonals.

3. OLED.
Organic LEDs. Something in between, between the first 2 technologies. The image is formed using self-emitting diodes, which glow under the influence of electric current. As in plasma, each cell is an independent light source. So far, there are only a few serial samples of such TVs at very high prices. Developments in this area are carried out by LG and Samsung.

There are other types of televisions, such as projection laser televisions, but their development has already been discontinued.

Briefly about the advantages and disadvantages of each technology:

- relatively low production price, which allows manufacturers to get a fairly high profit and invest in production.
- The static method of image formation (without dithering) is good for displaying images and photographs.
- Great for a static image and not afraid of it.
- LCD TVs have high brightness and low power consumption
- High black level (from 0.02 nits in a UV²A-matrix with carpet backlighting to 0.2 nits in IPS).
- Long response time
- Lack of volume and depth of image
- Dynamic resolution without artificial tricks 300 - 700 lines.

- The total depth of the image. In general, when delivering quality content, the image on the plasma differs noticeably from that in the LCD: it has greater depth and color saturation, and has a pronounced volume effect.
- Low black level (0.008 nits in Panasonic 2012 models).
- Have a dynamic resolution without artificial tricks 1080 lines.
- Great for dynamic images (movies), well reveal high-quality content.
- Actually there is no response time.
- Loose viewing angles
- Absolutely not suitable for connecting to a computer due to image
retention - Photos show worse (since gradations are obtained by dithering)
- High power consumption, not all models have high brightness.
- High production costs, low margins - it is becoming increasingly difficult for manufacturers to stay afloat.

The latest TV imaging technology. Self-emitting organic LEDs are used. Like plasma, these are self-emitting light displays that do not require backlighting.
Now only a few serial samples have been released at a price ten times higher than similar LCD and plasma TVs, but LG promises that in 3 years OLED TVs of similar LCDs and plasma-diagonals will cost 1.5 times more.
- low response time and high contrast, like plasma, because there are no mechanically rotating molecules and constant illumination, as in LCD.
- profitability
- wide viewing angles.
- different degradation of pixels over time (the same as in plasma, which results in image retention and pixel burnout). Now they are trying to compensate for this programmatically.
- Low service time: about 10,000 hours (for example, LCD - 60,000 hours, plasma - 100,000 thousand hours).

II Image Characteristics

Choosing a new TV, I came to the conclusion that some characteristics of the image can be changed, some cannot.
Measured characteristics:
- Black level (MLL, Minimum luminescence level) - the black level that the TV shows when the signal 0 is sent. [Nit]
- Brightness - the brightness level that the TV shows when the signal 255 is applied to it.
These 2 characteristics measured together when the “chessboard” (ANSI method) is displayed on the TV - the alternation of black and white areas. The brightness of each section, the arithmetic mean of the brightnesses of the black and white areas, is calculated.
- Contrast. The difference between the arithmetic mean of black and white areas when black areas are taken as a unit.
The ANSI contrast of IPS matrices is ~ 1000: 1, S-PVA - 3500: 1, UV²A - 5000: 1, plasma - 12000: 1.
- Color accuracy (DeltaE, deviation from the standard). A signal is input, an output signal is measured. The greater the deviation, the less accurate the color reproduction. It is believed that the naked eye is unable to detect a deviation of DeltaE <3, and zero indicates perfect color reproduction.
- Viewing angles. The smaller the viewing angle of the matrix, the more color is distorted. The smallest angles have LCD S-PVA matrices. The largest are plasma panels.
- Dynamic resolution. As you know, almost all TVs have a static resolution of 1080 lines (1920x1080 pixels), but the dynamic resolution (what the TV shows when the screen is moving) is often different. For this purpose, LCD-TVs introduce flickering backlighting, frame interpolation and other tricks.

Subjective characteristics
. These include the volume of the image, which is formed by a combination of black level and color saturation, the cinematography of the image, the effect of presence.

Thanks for attention.
If the article seems interesting, in the next part I will write about choosing a diagonal, 3D types, their practical differences, about image interpolation and try to debunk some myths.

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