Ultimate LED backlight system

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Ultimate LED backlight system

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TVs.

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

Hello, dear habra community.

I hope that this article can help people like me – those people who choose a TV, but do not know much about the subtle technical issues in this area. I would like to share with you my thoughts and practical conclusions about choosing a large and high-quality TV.
For the last 3 years I have been watching 42″ LCD CCFL (this is when the image is formed by polarized light from fluorescent lamps, passed through filters). In 2009There was no 3D yet, and thin LED-backlit TVs were just appearing and costing dishonest money. It was bought without much agony 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 have the necessary knowledge in this area. I knew for sure that I wanted a larger diagonal and deeper blacks.

After studying the materiel, I clarified some points.

I Imaging type.

Today there are 3 types of imaging on modern televisions:

1 LCD.

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

1.1 Types of LCD 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 source, it is necessary to designate 2 types of backlight:
a) CCFL, it is also a cold cathode. A subspecies of thin fluorescent lamps located behind the matrix.
Advantages: uniform illumination.
Disadvantages: large thickness, power consumption, impossibility of local backlight control.
b) LED – light emitting diodes. Currently, cold cathode televisions have been 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 need to be said about the local control of the backlight and the division of the LED backlight. LED backlighting is divided into 2 types: edge (aka 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 LCD pixels do not emit light on their own, they require a backlight (as discussed above) that is always on. Enclosed crystals still transmit light, so it is impossible to achieve low black levels (the lower the better) and contrast transitions in edge-lit systems. The highest level TVs use carpet backlighting (when the LEDs are located directly behind the matrix). This improves backlight uniformity and introduces segmented backlight control, where individual diodes that are responsible for areas on the screen can dim the brightness depending on the scene on the screen. In fact, only 2 series have carpet lighting – 9Philips 9th series and Sony 9th series. The LG 9 series also has carpet lighting, but its implementation is worse than the edge lighting of competitive solutions.

Backlight irregularity.

Due to the fact that the LEDs are arranged at regular intervals (scattering and many other factors contribute), in almost 100% of cases, LCD TVs with LED backlighting have uneven backlighting (clouding) – when areas that should remain black have different grayscale.
The problem is partially solved by segmented LED backlighting.

1.2 Types of matrix LCD TVs with LED backlight.

I will not go into details of image formation by different types of matrices, but will briefly describe their main advantages and disadvantages.
a) IPS (currently produced only by LG). Matrices that, in my opinion, are ideal for low-end and mid-range TVs.
Advantages: large viewing angles.
Disadvantages: high black level (~ 0.16 nits), long response time.
They are installed in LG 3-9 series TVs (that is, in fact, in everything, without separation by levels), Philips 4, 6 series, Panasonic of various variations and many others.
b) S-PVA (manufactured by Samsung). Matrices for TVs of classes above.
Benefits: deeper black (0.05-0.1 nits depending on backlight implementation).
Installed in Samsung 7-8 series TVs, Sony 7-8 series, Philips 7-8 series and some others.
c) UV²A (Sharp). In my opinion, the most perfect type of matrices.
Benefits: more angles than S-PVA (but less than IPS). Deepest black level (0.02 – 0.06 nits)
Drawbacks: Sharp does not produce enough of them.
Installed in Philips 9-series TVs and top-end Sharp series.

2. Plasma.

There are a lot of myths and misconceptions associated with this word. Any uninformed seller will tell you that plasma is outdated. This is due to a set of stereotypes and problems that have taken place.
The image is formed by the glow of a phosphor under the action of UV rays.
Each plasma cell is an independent light source, so the TV does not require a backlight. Previously, plasma TVs had a very large thickness and cell size, so they were very bulky and 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 TVs do not have different types of matrix 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 unprofitability of production, competition from LCD TVs and their popularization. But plasma holds the first positions in large diagonals.

3. OLED.

OLEDs. Something in between the first 2 technologies. The image is formed using self-emitting diodes that glow under the influence of an 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 engaged in LG and Samsung.

There are other types of televisions, such as projection laser televisions, but they have been discontinued.

A brief summary of the advantages and disadvantages of each technology:

LCD:
Advantages:
— a relatively low cost of production, which allows manufacturers to get a fairly high profit and invest in production.
– Static rendering method (without dithering) is good for displaying images and photos.
– Great for a static image and not afraid of it.
— LCD TVs have high brightness and low power consumption
Disadvantages
– 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 the image
– Dynamic resolution without artificial tricks 300 – 700 lines.

Plasma
Benefits
— The overall depth of the image. In general, when delivering high-quality content, the image on a plasma differs markedly from that on an LCD: it has greater depth and saturation of colors, and has a pronounced effect of volume.
– Low black level (0.008 nits in 2012 Panasonic models).
– They have a dynamic resolution without artificial tricks of 1080 lines.
– Great for dynamic images (movies), well reveal high-quality content.
– Virtually no response time.
— Freest viewing angles
Disadvantages
– Completely unsuitable for connecting to a computer due to afterimage
– Photos show worse (since gradations are obtained using dithering)
– High power consumption, not all models have high brightness.
– High production costs, low margins – it is increasingly difficult for manufacturers to stay afloat.

OLED
The latest imaging technology in TVs. Self-emitting organic light emitting diodes 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 similar to LCD and plasma diagonals will cost 1. 5 times more.
Benefits:
– low response time and high contrast, as in plasma, because there are no mechanically rotating molecules and constant backlighting, as in LCD.
– economy
– wide viewing angles.
Drawbacks:
– different degradation of pixels over time (same as with plasma, which leads to afterimages and pixel burn-in). Now they are trying to compensate for this programmatically.
– Low service life: about 10,000 hours (for example, LCD – 60,000 hours, plasma – 100,000 hours).

II Picture characteristics

When choosing a new TV, I came to the conclusion that some picture characteristics can be changed, some cannot.
Measured characteristics:
– Black level (MLL, Minimum luminescence level) – the black level that the TV shows when the signal is 0. [nits]
– Brightness – the level of brightness that the TV shows when a signal of 255 is applied to it.
These 2 characteristics are measured together when a “checkerboard” (ANSI method) is displayed on the TV – alternating black and white areas. The brightness of each area is calculated, the arithmetic average of the brightness of black and white areas.
— Contrast. The difference between the arithmetic mean of the black and white areas when the black areas are taken as one.
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). An input signal is applied, the output signal is measured. The greater the deviation, the less accurate color reproduction. It is considered that the naked eye is unable to notice the deviation DeltaE < 3, and zero indicates the ideal color reproduction.
– Viewing angles. The smaller the viewing angle of the matrix, the more the color is distorted. LCD S-PVA matrices have the smallest angles. The largest are plasma panels.
– Dynamic resolution. As you know, almost all TVs have a static resolution of 1080 lines (1920×1080 pixels), but the dynamic resolution (what the TV shows when there is movement on the screen) is often different. It is for this purpose that flickering of the backlight, frame interpolation and other tricks are introduced in LCD TVs.

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

Thank you for your attention.
If the article seems interesting, in the next part I will write about the choice of diagonal, 3D types, their practical difference, about image interpolation and try to debunk some myths.

Broken TV lamp: cool idea

The best thing to do with a broken item or technique is to give it a second life. Broken TVs can be an attractive home lighting solution. This article will show you how to take apart a broken LCD TV or monitor and turn it into an amazing LED panel. It simulates daylight almost perfectly and is useful for photographers and filmmakers who need good lighting in their work.

Required materials and tools

LCD monitors and TVs are great daylight LED panels because they give the impression that the light is coming from far away. The main reason for this effect is the Fresnel layer that is inside these monitors. This design reduces the incidence of light, so objects located far from the light source are still well illuminated.

What you need for this project:

• screwdriver;
• LED strips;
• Faulty LCD TV or monitor.

The list is small, the task is simple, you can proceed to the guide below.

How to make a lamp out of a broken TV

Parsing involves removing the backlight from a damaged TV or monitor. They have a powerful white light inside, but they are also equipped with a Fresnel lens. This helps the backlight look very much like a real skylight due to the way it diffuses the light around the room.

1. Lay the monitor horizontally and unscrew all the screws on the rear panel. When you remove the plastic cover, you will need to unscrew all the screws from the inside and carefully remove all metal components and electronics. Be careful not to touch the boards as they may still be live in the capacitors. You will need to remove the LCD panel until the backlight panel itself remains.
2. The backlight panel usually has a diffusion layer, a Fresnel layer underneath, another diffusion sheet and an acrylic backlight. These are all very useful for your LED panel, but you will have to temporarily pull them out.
3. Now that all the layers have been removed, you have the metal backlight frame and its natural light. Newer models contain LED strips, but you will find small CCFL bulbs in older models.
4. When it comes to powering your future LCD panel, you have two options. You can keep the native LCD strips or CCFL bulbs, but that can be pretty dangerous if you don’t know what you’re doing. The electronics with them are quite complex, and they work with high voltage. The preferred option is to remove them and add your own high CRI LED strips. They often come with an adhesive back so they are very easy to install.