What Is The Difference Between An LCD And An LED Backlit LCD Display?

Recently I wrote an article about buying a great HDTV on a tight budget. Some commenters on that article noted that I didn’t entirely explain the difference between LCD and LED displays, and that there wasn’t any explanation on MakeUseOf.

This subject is complex because it’s simple. The differences between LED vs LCD TV are subtle, which can make it difficult to understand the difference. It’s an important distinction, however, because it can significantly impact image quality as well as price. I’m also going to explain the differences between LED displays – not all of them are built the same.

The Core Question – What’s LCD vs LED?

LCD, or Liquid Crystal Display, is the fundamental display technology used by most monitors, televisions, tablets and smartphones. It consists of a panel of liquid crystal molecules that can be induced by electrical fields to take certain patterns which block light or allow it through.

Color LCD displays have green, blue and red sub-pixels in each pixel. The intensity of light allowed through each sub-pixel is carefully controlled to create a detailed picture capable of displaying millions of different colors.

However, the crystals create no light of their own. It’s possible to light an LCD using reflected ambient light (the Nintendo GameBoy Advanced operated in this way) but all LCD HDTVs have a backlight which shines light through the display.

In the past, HDTVs used cold cathode fluorescent lamps to provide this light. However, manufacturers noticed that using Light Emitting Diodes would provide equal light with less energy. It was also possible to turn individual diodes off when no light was needed, something that’s not possible with CCFL lighting.

Because the addition of LEDs for backlighting was the new feature, this was used to describe the new televisions. But the new LED TVs still use an LCD display, just like the previous models lit by CCFL tubes.

So, Why Is LED Better?

CCFL tubes can’t be switched on or off while a display is turned on and can only be arranged in vertical or horizontal lines. This creates picture quality problems. Since the lighting is never turned off, dark scenes are hard to render properly, and the arrangement of the CCFL tubes can cause parts of a display to appear brighter than others.

LEDs, on the other hand, can be quickly switched on or off. This allows much better control of light. They also can be arranged in a grid across a display or in a ring around a display, which offers theoretically better light distribution. Finally, LEDs do not consume as much energy.

There are different types of LED displays, however, and each has different traits. I’ll explain each.

Edge-Lit LED

The image above provides a basic example how an edge-lit display works. In this instance a green LED is shone inwards on a Christmas tree pattern. The light is guided along that pattern and creates a profile. In an edge-lit HDTV there are also light guides, but instead of trying to create a specific pattern they attempt to distribute light evenly across the interior of the television.

This technology can be used to create extremely thin displays, is generally low on power draw and relatively inexpensive compared to other LED variants. If you see an LED-backlit HDTV for a low price there’s a good chance it is edge-lit.

Edge-lit displays usually do not manage to be entirely even in their light distribution, so they suffer from uniformity issues (i.e. parts of the image appear brighter than others.) Some models offer local dimming. This feature precisely controls the light output of LEDs to display deeper black levels.

Full Array LED

A full array LED display has a grid of LED lights behind the LCD display. They shine directly outwards, creating a bright and usually uniform picture. Most televisions with a full array are expensive, enthusiast models that offer local dimming. This can provide excellent black level performance.

There are, however, a few LED sets with a full array that lack local dimming. A television set up this way will provide the uniformity benefits of LED, but probably won’t offer black levels that are much, if any, deeper than a good display lit by traditional CCFLs.

RGB-LED

This rare technology uses colored LED lights to provide additional color and lighting control. This creates very precise colors and can also provide better detail in scenes with a lot of contrast. RGB-LED is technically a modifier of the other two types – there can be edge-lit and full array versions – but most displays with this type of backlight are full array.

There are not a lot of displays that use this technology. Dell is known to offer RGB-LED in its workstation laptops and there are some high-end televisions and monitors that offer this, such as Sony’s $5000 Bravia XBR8.

Displays with RGB-LED are almost always very, very good, but most people can’t justify the extra cost.

Conclusion

I hope this has clarified the difference between LCD and LED – or, rather, highlighted the fact that it’s not a difference so much as a confusion of terms.

If you’re wondering if LEDs are worth it over non-LED displays, the answer is that it depends. There are other competing technologies, like Plasma and OLED, which operate differently and have different traits.

Individual product quality is also a big deal. Some of the best displays in the world use LED backlighting – but there are also some very poor displays that use this technology, as well.

Image Credit: Gianluca Bertoncelli, LGEPR, Garrett Mace, Windell Oskay

Originally published on MakeUseOf.com. Great site, check it out.