LED vs. LCD TV: What you need to know ?

You walk into your local electronics store looking for a new TV and come across a thing called an "LED TV". Which then leads you to ask: "Is that the same technology they use for the giant screens at football games?" And the answer, quite simply, is no.

While the giant display in a sports stadium, for example, is made up of thousands of LED's that are used to directly produce an image, "LED" TVs are actually LCD's. That's right, they're not LED TVs at all. These "so-called" LED TVs use a series of LED bulbs to light up the screen. But what is back-lighting anyway?

Why do LCD screens need a backlight?

As a consumer technology, LCD has been in widespread use since the early 1970s when it first appeared in digital watches. As its name suggests, Liquid Crystal Display is a fluid which has been sandwiched between two plates, and it changes when a current is applied to it.

While we've had black-and-white LCD's for years, color LCD's are a lot more recent, but the technology is the same. As we all know, you need to press a button to read a watch in the dark, and an LCD TV is no different. It needs a light source because it emits no light of its own.

 

What types of back-lights are there?

At present there are two common methods of back-lighting in LCD flat panels: Cold-cathode fluorescent lamp (CCFL) and LED (light-emitting diode). CCFL used to be the most widespread method of back-lighting for LCD TVs, and consists of a series of tubes laid horizontally down the screen.

LED back-lighting is now very common and has been in use in TVs since 2004 when it first appeared on a Sony WEGA. Though there are several different ways of back-lighting using LED's (as we'll explain shortly), the idea is the same: A lot of LED bulbs are used to light the screen.

 

Backlit (full array) or edgelit?

There are two different types of LED back-lighting: Backlit and edgelit. The main advantage of backlit is that it can be used to increase contrast levels by turning selected LEDs off through a function known as local dimming--thus increasing the black level in parts of the picture.

In comparison, edgelit's key advantage is that it can be used to make TVs that are incredibly thin--the LEDs are at the side and not behind the panel. Local dimming is now available for edgelit TVs, too, but with much fewer "dimmable" segments compared with a backlit panel: Tens versus hundreds.

The picture quality of LED-edgelit TVs has improved significantly over the past few years, delivering better contrast and deeper blacks. On the other hand, as LED-backlit panels such as the Samsung S9 and LG LA9700 ultra high-definition (UHD) TVs are costlier to manufacture, they are becoming increasingly rare these days.

 

White or RGB light?

White LED is very similar to CCFL because LED uses a blue light source that is made to look white by the presence of a sulphur coating on the bulb. As a result, the TV will potentially be stronger in the green portion of the spectrum. But as some CCFL technologies enable better red and blue response, better white LEDs could also be possible.

RGB LEDs, on the other hand, are potentially capable of a broader color range because they use three LEDs colored red, blue and green. Its proponents argue that there is less of a green "push" as a result and the color spectrum is more evenly distributed.

It has been some time since a TV manufacturer launched an RGB LED TV. The last model was the 2009 Sharp LC-65XS1M, although Mitsubishi has recently showcased an RGB-based UHD TV at the Ceatec tradeshow in Japan. What's more, the Mitsubishi display uses a red laser source (with green and blue LEDs) instead of RGB LEDs.

 

LED-edgelit technology under the microscope

Most LED-edgelit panels consist of two major components: A long LED module with a row of tiny white diodes and a thin screen-sized plastic sheet known as a light guide plate. Two LED modules are deployed along the top and bottom of the panel. The combined light output is then funneled and spread out across the screen.

Technically, an edgelit LED system lacks finer back-light control compared with the backlit version. Uneven back-light uniformity is another common shortcoming. To put this into perspective, a backlit panel can turn on selected LEDs to bring out the sparkle of stars in a galaxy while switching off the remaining bulbs to produce deep blacks for the background. Edgelit panels are usually less capable in this aspect.

 

Is the price premium for LED worth paying?

With LED TVs now widely available and their traditional LCD counterparts almost extinct, this question is largely irrelevant for the key electronics brands. You can probably still find some LCD TVs from smaller domestic manufacturers, but the price savings are minimal with LED TVs going for as little as S$300 (US$241.04) these days.

The few LED-backlit screens we have seen so far still have a slight advantage in terms of the overall picture quality, and while we still prefer plasma panels, the combination of slim aesthetics and sharp visuals in the latest LED TVs will find favor with most people. If you're looking for a further explanation of how LCD screens work, check out this video on the 3M site.

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