Giz Explains: What’s So Great About LED-Backlit LCDs

Giz Explains: What’s So Great About LED-Backlit LCDs
LED-backlit LCDs are where TV’s future and present meet—they’re the best LCDs you’ve ever seen, but they’re not as stunning as OLED displays, which will one day dominate all. They’re not cheap, but they’re not ludicrous either. Most importantly, they’re actually here.

I’ll CC You in the FL
With LCDs, it’s all about the backlighting. This defines contrast, brightness and other performance metrics. When you watch plasma TVs, OLED TVs or even old tube TVs, there’s light emanating from each pixel like it was a teeny tiny bulb. Not so with LCD—when you watch traditional LCD TV, you’re basically staring at one big lightbulb with a gel screen in front of it.

The typical old-school LCD backlighting tech is CCFL—a cold cathode fluorescent lamp—which is an array of the same kind of lights that make people’s lives miserable in offices around the world. The reason they aren’t the greatest as backlights for TV watching is that they light up the whole damn display. Because LCD is just a massive screen of tiny doors that open and close, light inevitably leaks through the closed doors, when they’re trying to show black, resulting in more of a glowy charcoal. Check out this shot from Home Theatre mag to see what I mean:

LEDs (light emitting diodes) are different from say, an old school incandescent bulb, which heats up a filament to generate light, in that they’re electroluminescent—electricity passes through a semiconductor and the movement of the electrons just lights it up. Instead of having one lightbulb in the bottom of the screen, shining up through all of the LCD pixels, you can have arrays of LEDs that shine through smaller portions of the LCD screen, leaving other portions in the dark, so to speak.

OLED—”organic light emitting diode”—is slightly different. Since the electroluminescent component is organic and not a chip, each point of light can be much tinier. That’s why an LED TV still needs the LCD screen in front: there’s no way to have a single LED per pixel unless the screen is huge, and mounted to the side of a building in Times Square. OLEDs don’t: HD OLED displays are made up of red, green and blue dots, no LCD panel required.

LED Is As LED Does
So, Samsung’s term “LED TV” is more accurately—and more commonly—described as an LED-backlit LCD. But not all LED displays are created equal.

There are two major kinds of LED backlighting: Edge-lit and local dimming. Edge-lit displays are what they sound like—the LEDs are arranged in strips running along all four edges of the TV, like you can see in this gut shot from Cnet. A light guide directs the glowyness toward the centre of the screen. The advantage of edge-lit displays is that they can get incredibly thin, are 40 percent more power-efficient than regular LCDs and are a bit cheaper than local-dimming TVs. But because they’re still shooting light indiscriminately across the LCD panel, they can’t pull off the black levels that a local dimming backlight setup can.

LED backlighting of the local dimming variety is how you build the best LCD TV in the world. It’s called local dimming, as you probably guessed, because there are a bunch of LED bulbs—hundreds in the Sony XBR8—arranged in a grid behind the screen. They can all be dark or brightly lit, or they can turn off individually or in clusters, making for the actual Dark Knight, rather than the Grayish Knight you’d see on many cheaper CCFL LCDs. Sets with local dimming are pricier than edge-lit—the Samsung’s local-dimming 46-incher started at $US3,500, versus $US2800 for one of their edge-lit models. They are thicker too.

What Colour Is Your LED?
The colour of the LEDs matters too, separating the best LED-backlit LCDs from the the merely great. Most LED sets just use white bulbs. The reason Sony’s XBR8 started out at $US5,000—as much as Pioneer’s king-of-TVs Kuro—is because it uses tri-colour LEDs in an RGB array. In each cluster, there are two green bulbs next to one red and one blue (greens aren’t as bright). The result is high contrast plus super clean, incredibly accurate colour.

LED displays are getting cheaper, more quickly than originally expected, so we could see them go mainstream sooner. You already see the lower-end edge-lit LED tech used in mainstream stuff—MacBook Pro and Dell’s Mini 9 to name a couple. Which is a good thing, since the prophesied ascendancy of OLED in 2009 completely failed to happen. So we’ll have to make do with LED in the meantime. Just be sure to find out what kind when you’re buying.