Edge-lit vs. Local Dimming
Buying a new television, despite the myriad of specifications, technologies, resolutions, and other factors, doesn’t have to be a bewildering quest. With the shuttering of plasma technology by Pioneer, Samsung, and others, the only remaining mainstream technology is LCD, which continually gets better and better. Virtually all mid-tohigh-range LCD displays now use LED backlights (instead of CCFL), with either local or edge-lit dimming to enable deeper blacks and richer, brighter colours. 3D didn’t take off as manufacturers and studios wanted but has nonetheless, helped to improve performance by increasing refresh rates, colour gamut, and other specifications that are also used for 2D video. Starting off with resolution and ending with budget, the list of questions a consumer needs to ask is now much more succinct. At their core, all LCD displays consist of a white backlight sitting behind an RGB (red, green, blue) LCD panel. The backlight shines light forward, while the LCD controls the passage of the backlight to illuminate each individual colour pixel. In older LCD displays, the backlight was often a single unit which could not vary its light output across the screen and more importantly, not turn off. This in turn, made it very difficult for older LCDs to deliver truly dark blacks, often displaying them as dark grey or blue. One advantage of the now defunct plasma technology, by virtue of its process, was its ability to not illuminate individual pixels as needed. Advancements in LCD backlight technology, beyond moving to higher quality LED backlights, now include edge-lit and local dimming, splitting the backlight into multiple zones for more refined control.
The backlight, therefore, is now the one of the specifications that has the largest effect on picture quality. Edge-lit displays are the cheaper of the two versions and use backlights arranged around the edge of the display. Unfortunately, there are numerous edge-lit backlight configurations used by each manufacturer, with varying picture quality, depending on the price of the TV. If the edge-lit backlight is only along one edge, it effectively creates rows or columns of backlights. If more backlights are used, such as top/bottom, right/left, or all four sides, this increases the effective addressable backlights areas. The more precise the edge-lit backlight control, the darker the image can get, and the higher the resulting contrast and subsequent picture quality.
Backlights can further be re-