It’s the latest innovation on the flat panel TV scene. It’s touted as giving better blacks, crisper contrast and a more complete colour range. What is it? It’s the LED TV and it’s being pushed hard by TV manufacturers around the world.
But are LED (Light Emitting Diode) TVs really any better than their LCD forefathers? In a word – yes! To find out why, read on…
To understand why LED TVs are better than standard LCD TVs you first need to know how an LCD TV works.
LCD TV screens are a matrix of liquid crystal. When electricity is passed through this matrix individual cells within it untwist to filter white light from a central light source behind the screen. Depending how far they untwist, they filter out differing wavelengths and create different colours. The cells themselves do not produce light.
It’s All in the Light Source
The light source in standard LCD TV is provided by Cold Cathode Fluorescent Lamps (CCFL) – basically a set of fluorescent tubes that are always on when the TV is in operation.
There are two main problems with TVs that use CCFL lighting:
- They cannot reproduce true blacks. When the TV wants to show a black night sky, say, the liquid crystal cells twist all the way closed in an attempt to block all the light that the CCFLs are emitting. They do a pretty good job at this, but as the CCFLs are always on some light bleeds through the picture and causes blacks to be somewhat grey. This has the added disadvantage of making picture contrast appear less crisp than it might be.
- Their colour saturation is limited. The type of white light produced by CCFLs has a narrower spectrum than some other white light sources and the range of colours it can be split into (known as its colour gamut) is consequently limited.
The first thing you need to know about LED TVs is that they are not really LED TVs at all, in that they do not use a matrix of LEDs to create their picture. Rather, they are a form of LCD TV, the only difference being that instead of using CCFLs they use a collection of LEDs as their light source.
Advantages of a LED Light Source
Instead of a row of CCFL tubes behind your TV picture, imagine a panel dotted with as many as a thousand individual LEDs. Now imagine that these LEDs can be dimmed or turned off in groups (a process known as localised dimming).
The advantages of using LEDs in this manner are:
- Rather than trying to create blacks by just closing up the liquid crystal matrix, areas of LEDs behind that matrix can be selectively turned off. This reduces light bleed, gives truer, deeper blacks and improves picture contrast.
- The white light emitted by LEDs has a broader spectrum than that emitted by CCFLs and can be split into more colours. This increases the colour gamut and produces a richer colour experience.
Two Types of LED TV
The type of LED TV described above is known as a back-lit LED TV. There is, however another form of LED TV on the market known as an edge-lit LED TV.
Instead of a panel of LEDs behind the picture, edge-lit LED TVs have a boarder of LEDs around the outside of the liquid crystal matrix. The light from this ring of LED’s is then diffused by a special panel to provide a uniform light source behind the picture.
Edge-lit technology, as it does not require a panel of LEDs, enables the production of ultra thin flat screens. However, the selective dimming of the back-lit LED TVs with their truer blacks and better contrast is absent. Further, the type of LED used in edge-lit TVs produces white light of a narrower spectrum than those used in back-lit TVs and colour saturation is therefore reduced (though it’s still better than a standard LCD TV).
Further Advantages of LED TVs
Beyond the picture quality advantages, LED TVs are more energy efficient and can use up to 40% less electricity than a standard LCD TV.
CCFL tubes become dimmer over long periods, reducing picture quality. The performance of LEDs, however, does not degrade with time.
Claims have also been made for the environmentally friendly nature of the new generation of TVs as LEDs do not contain the toxic mercury used in the manufacture of CCFLs. However, LEDs do contain the toxic elements gallium and arsenic and it is debatable whether or not they are, on balance, any more environmentally friendly in this respect.
LCD TVs will be on the market for a long time yet, and some of them are very good. But if you want blacker blacks, more colours and better contrast consider the next generation of TV technology and check out a LED TV.How to Choose a LED TV,