To help us provide you with free impartial advice, we may earn a commission if you buy through links on our site. Learn more

How LED TV works – behind the LCD TV technology

We find out how LED TV differs from what you might call an LCD TV

There is, actually, no such thing as an LED TV. You might have a TV that claims it’s an LED TV on the box, or your mates might have mentioned they have one of those “new LED TVs” but the truth is, that name is an accident, little more than something that happened because people thought it was easier to talk about LED TVs than LCD TVs with LED backlights.

LCD TVs were always a bit lighter and less bulky than plasma screens. They generally involved a bit less glass and didn’t need as much room for air ventilation and fans like plasmas did. That said, early LCD TVs were still pretty huge, but when manufacturers started using LEDs for illumination suddenly it was possible to make a TV that was almost impossibly thin.

The biggest problem with producing super-thin TVs, is that it was more about aesthetics than picture quality. Thin TVs were about attracting people who wanted to mount their television on a wall, thus being something of a statement when visitors came over.

The good news is that employing LEDs for the backlight within LCD TVs brought other advantages besides that new, anorexic look.

[[IMG ID=”222250F”]]
One big benefit of LED is that TVs can be a lot slimmer


The TVs that were most dramatically reduced in size were those that switched from a backlight positioned behind the LCD panel, to one located at the sides – usually the left and right of the panel. This means that the large tubes that were previously behind the LCD panel were gone, and everything could be packed closer together.

What’s more, the move to LEDs meant that there was less heat generated too, so there was less need for internal airflow, offering further size reduction.


Manufacturers had another reason to love thinner and lighter TVs though. With the size and weight reduction they become easier, cheaper and more environmentally friendly to ship around the globe. LEDs are better for the environment than the old CCFL fluorescent tubes that used to be found in LCD TVs because they don’t contain so many nasty chemicals, and also use less power. And that cost reduction means the public loves them too. Indeed, LED lit LCD TVs were often surprisingly cheap, giving customers exactly what they wanted.


There are three main types of LED “backlight”. The first isn’t a backlight, but a sidelight and it is the technology that allows TVs to be very thin indeed. In this system, LEDs are placed down the side of the TV and then a complicated diffuser takes the light and distributes it across the whole LCD panel. This technology is very good for making thin TVs, but it does create problems when it comes to even lighting. Early edge-lit LCD TVs were especially bad when it came to the corners and edges. It was common to see very bright spots in these areas, especially when the screen was showing a dark image, or total black. For the most part, these TVs were not aimed at picture quality enthusiasts, but at people who were more concerned with impressing visitors.

[[IMG ID=”222256F”]]
Edge-lit screens have LEDs around the side of the screen

A better LED backlight system is the “full array”. These are made up of thousands of individual LEDs that are mounted directly behind the screen. They are dimmable as a whole, which means that in dark scenes you shouldn’t see washed out grey instead of black. These are also more even, so there shouldn’t be bright spots anywhere on the TV, and there won’t be noticeably more brightness in the corners or edges. Although this kind of backlight doesn’t offer massive control, it still add to the cost of the TV because it’s reasonably expensive to make.

[[IMG ID=”222247F”]]
Both full and local dimming sets have an array of LEDs behind the screen

The third, and most impressive form of LED lighting comes from something called “local dimming”. This gives a lot of control over which area of the screen has illumination and which does not. So mixed scenes are less of a problem for locally dimmable TVs. There is quite a wide range of qualities available though, because the number of LEDs used will greatly affect how much control the TV has over which parts can be dimmed.

Local dimming is very good, but unless you have a lot of LEDs and complete control over them you will sometimes see problems. For example, a shot of stars in space might mean that the points of light making up the stars have a halo effect around them, making the scene look different to how it would on a plasma TV. More expensive TVs have better control, so if you’re keen on picture quality, you need to spend a bit more.


With LED lighting came the option to have what is known as a scanning backlight. This is actually a very important picture quality improvement for LCD screens. The idea is that the backlight strobes very quickly, quicker than the eye can see and the result is much better black levels along with greatly reduced motion blur.


The CCFL backlight is basically dead now, so most LCD TVs are now lit by LEDs. This is a good thing, as most TVs look better with LED backlights than they would with the inflexible fluorescent tube system.

LED backlights can only get better. As processing improves and advances to LED sizes are made, along with brightness increases, the quality of LED backlights will get better. High end LED-based TVs are now very nearly at the point where they can compete with plasma TVs in terms of contrast.

[[IMG ID=”222253F”]]
Until OLED really takes off, LED is the future of TV

Of course, with OLED on the way, the idea of a backlight might be foreign to TVs in five years time, because OLEDs produce their own light and need no help from LEDs at all. This is why OLED TVs can be the thinnest and most impressive on the market, and can be produced in all sorts of weird shapes.

For now though, an LCD TV you buy will almost certainly feature an LED backlight. For quality, get one that has local dimming but for bargain-basement pricing and supermodel thin looks, get an edge lit model.

Read more