Scientists have warned that rapid strides in the development of artificial intelligence and...
All so-called LED TVs are really just LCD TVs that use LEDs for their backlight. This backlight creates the light that allows the LCD to create an image. However, there are multiple ways these LED backlights can be arranged, and that arrangement can have a dramatic effect on picture quality.
So here's your guide to all the different versions, with some funky illustrations, too.
C-ya CCFL, hellllo LED
Traditional LCDs use CCFLs, or cold-cathode florescent lamps, as their backlight. While cheap, they're not as energy efficient as LEDs. More importantly, all contain mercury, and aren't able to do some of the fancy area-lighting of which some LED backlit models are capable. Because of these issues and the falling prices of LEDs, CCFL backlit LCD TVs will disappear entirely very soon. In 2013 LG and Sony proudly announced they'd stopped using CCFL backlights altogether, even in their cheapest TVs, in favor of LEDs. Vizio, Samsung, Sharp, Toshiba, and Panasonic weren't as vocal about it, but none has announced any non-LED-backlit TVs for 2013.
Most LED LCDs on the market today are edge-lit, which means the LEDs are in the sides of the TV, facing in toward the screen. In the image at the top, the LED strips are above and to the side of this exploded-view of an LCD panel. There's a close-up view here (full article with more images here).
There are a few models that are have their LEDs arrayed on the back of the TV, facing you. These are less common, though are making a comeback in the form of cheaper, but thicker, mostly low-end LED LCDs. There are a handful of high-end TVs that use full-array LED backlighting in a slightly different way, which we'll discuss later.
Edge-lit LEDs have a light guide that helps reflect the light from the edges of the TV somewhat uniformly across the screen. They do this with varying success. To give you an idea of what I'm talking about, here's an incredibly well-drawn diagram from that article that shows how these light guides work.
This wondrous diagram shows a top-down cutaway view of the right half of an edge-lit LED LCD. The LED (yellow here, because white doesn't show up on a white background) fires along the width of the TV. The light guide (circular parts) reflect this light towards the screen. Done perfectly, the center of the screen (where the guide is tallest), is just as bright as the edges.
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Because the light is brightest nearest the LEDs, it's common for edge-lit LED LCDs to have poor uniformity. This is especially noticeable on dark scenes, where areas of the screen will appear brighter than others. Corners or edges can have what looks like tiny flashlights shining on the screen. Check out Is LED LCD Uniformity a Problem? for more.
Each manufacturer has a preferred method for edge-lighting, but some models may feature one type, while other models feature another type. Generally speaking, the fewer LEDs the cheaper the TV is to produce. Fewer LEDs also mean better energy efficiency, but LED LCDs are already so efficient that this is a tiny improvement. Unfortunately, specific details about where a TV's LEDs are located (beyond "direct" or "edge"), the number of LEDs, and other useful information about the backlighting, are rarely listed on a TV's spec sheet.