What is the difference between a QLED and OLED TV?


by Steve Withers Feb 23, 2017 at 8:03 AM

  • Acronyms are common in the world of AV but these days there seem to be more than ever and the latest to join the growing list is Samsung's QLED but what is it and how does it differ from OLED?
    QLED or OLED, it's easy for consumers to confuse the two and, if you were being cynical, you might think that's the reason Samsung have chosen the name. However, whatever the reasons for the choice of name, OLED and QLED are very different, with one being a relatively new approach to delivering a TV picture and the other being a refined version of a tried and tested technology.
    The main difference between the two types of TV is how they create the light that makes up the picture. OLED, which actually stands for organic light emitting diode, is a self-illuminating technology, which means that each pixel making up the picture emits its own glow when electricity is passed through the organic compound from which it's composed. In that sense an OLED TV is very similar to a plasma TV and thus it shares many of the older technologies strengths and weaknesses. The self-emitting nature of OLED means that when the electrical current to the pixel is stopped there is absolutely no light, resulting in the deep blacks of which OLED is justifiably famous. In fact the blacks are even better than those of a plasma TV because with an OLED there is no after-glow, each pixel goes black instantly.

    MORE: What is an OLED TV?

    By comparison QLED is a marketing term and a QLED TV still uses a traditional LCD panel with an LED backlight, whether that backlight is at the edge or to the rear. The image is created by passing the light from the LEDs through the panel and, as result, the black levels are far less impressive when compared to an OLED TV. To improve their black level performance LCD TVs use a number of technological developments, including vertical alignment (VA) panels and local dimming. The use of a VA panel does improve the black levels but at the expense of the off-axis performance.

    Local dimming involves breaking the picture up into zones and turning them on or off depending on the image, this does improve the blacks but also results in haloing where a bright object glows because it crosses over two zones. The solution is to increase the number of zones because the more zones, the less likely there will be haloing. There have been LCD TVs released with over 600 local dimming zones but to put that in perspective, an OLED TV with its self-illuminating pixels effectively has over 8 million dimming zones. So an OLED TV can not only deliver deeper blacks but it do so with far greater accuracy.
    If Samsung's new QLED TVs just use an LCD panel with LED backlighting, why the new name? Well the clue is the 'Q' in the name QLED, which stands for quantum dot (QD). This is a nano coating over the LEDs that make up the backlight and although quantum dots aren't new, Samsung feel they have extended their capabilities to deliver a LED LCD TV that can compete with an OLED TV. First of all the latest quantum dots not only deliver a much wider colour gamut but they can also deliver increased brightness and greater energy efficiency.

    MORE: What are Quantum Dots (QD)?

    However Samsung have also developed a new dual pixel structure in their LCD panels that, when combined with the quantum dot coating on the LED backlight, results in a wider optimal viewing angle than was previously possible. Samsung now believe that their QLED TVs can deliver an off-axis performance in terms of colour accuracy that is comparable to OLED. A very wide viewing angle is a major strength of an OLED TV but has always been a limitation of LED TVs that use a VA panel. Samsung hopes that QLED will allow them to compete in this area, although how effective it actually is remains to be seen.

    MORE: What is High Dynamic Range (HDR)?

    However the one area where an LCD TV does have a clear advantage over OLED is in terms of peak brightness and this is especially important when it comes to High Dynamic Range (HDR). The most recent generation of OLED TVs are much brighter than they have been in the past, with LG claiming their latest models can hit 1,000 nits of peak brightness in an inaccurate vivid mode and Panasonic claiming that their new OLED TV can hit about 800 nits whilst retaining colour accuracy. Conversely Samsung's new QLED TVs can deliver over 1,500 nits of peak brightness and a colour gamut that is wider than DCI-P3, resulting in the ability to deliver 1,000 nits and DCI-P3 accurately.

    MORE: What is Wide Colour Gamut (WCG)?

    The combination of peak brightness and colour gamut is referred to as the colour volume and Samsung's QLED TVs are designed to deliver as large and as accurate a colour volume as possible. By comparison an OLED will struggle to deliver the full 1,000 nits with anything approaching accuracy and with brighter peak highlights the image will lose detail in the colours, which is often referred to as clipping. A brightly lit coloured object will retain is saturated colours on the QLED TV but appear washed out on the OLED as it struggles to deliver the peak brightness and full colour gamut. So whilst OLED has the advantage in terms of the darker part of the image, QLED has the edge when it comes to the brighter part of the picture.

    We mentioned earlier that OLED shares some of the strengths and weaknesses of plasma and one of those weaknesses is image retention and screen burn. Although the manufacturers go to great lengths to mitigate this issue, as the panels get brighter there is still a risk of image retention and even screen burn. So when it comes to gaming in particular, OLED owners need to be careful, especially with HDR gaming. There are no such issues with LCD panels, so much so that Samsung are happy to offer a ten year guarantee against screen burn.

    As things currently stand OLED is a genuinely new display technology and one day we might see QLED evolve into an equally new technology whereby each pixel is composed of individual nano LEDs. However for the time being QLED is an LCD panel with a quantum dot filter and an LED backlight, and the name is a marketing term used by Samsung.

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