Direct-LED backlight vs Edge-LED backlight in TVs
Of course, the TV choice depends on the image quality. In turn, image quality depends on the quality of the LED backlight. As known, LCD pixels do not emit light and require a backlight. LED backlight is most popular in modern TVs. It's subdivided into Direct LED and Edge LED. Direct LED uses LEDs behind the matrix across its surface, and Edge LED uses LEDs along the perimeter of its side surface. In this case, the light falls on a special splitter, then redirected to the diffuser and dissipates over the surface of the matrix.
Direct LED
The LED strips inside the matrix container are arranged parallel to each other. The distance between the LEDs is 3 to 5 inches, depending on the type of LED strip.
PROS: - uniform backlight. CONS: - relatively large thickness of the matrix. Uniform backlight requires a high-quality optical diffuser that affects the thickness of the matrix container. Therefore, these models are significantly thicker compared to Edge LED.
Edge LED
Of course, this backlight is the cheapest and easiest. But LEDs for backlight are located at the edges behind the screen. The number and location of LED strips is the main difference. Budget models use only one or two LED stripes on the bottom, top or side. Expensive 4K TVs often have LED stripes on all four edges (all sides configuration).
Typically, companies indicate a backlight configuration - all sides, only on one side (usually on top or bottom) or on two sides (usually on the sides). Of course, all sides configuration is optimal for local dimming and ensures maximum depth and uniformity of the black level on the screen. But today it's less popular because of the high cost that is due to the large number of LEDs. PROS: - thin matrix; - high brightness; - low energy consumption. CONS: - excessive lighting on the edge of the screen; - models with Edge LED are expensive compared to Direct LED; - uneven LED backlight.
Improved LED backlight
Of course, competition between companies is accompanied by a continuous improvement of technology. Therefore, today manufacturers use various innovative solutions, improving Direct LED and Edge LED. For example, FALD (full-array local dimming) and NANO Full LED are improved versions of Direct LED. LED Plus, in fact, Edge LED with the option of extended local dimming. Direct LED backlight is used in 9 series of Philips and Sony models. LG TVs of 9 series are also equipped with a Direct LED backlight, but its quality is lower. LED backlight is always on, and crystals pass light even when closed. Therefore, this technology does not provide the low black level and the high contrast for color transitions (the picture quality is inversely proportional to the black level). This problem is solved by companies with the help of Local Dimming technology that provides independent on/off of individual groups of LEDs in different areas of the screen.
Pros and cons of the Direct-LED and Edge-LED backlights are perfectly demonstrated on this video. Read the full article