There may only be one letter between these two technologies, but the way they deliver an image is vastly different. We illuminate the bright lights and gloomy darks of OLED and QLED TV screens...

These are halcyon days for TV technology. Ultra HD 4K is now pretty well established, HDR is beginning to make headway, and streaming puts a near-infinite supply of content at our fingerprints all day, every day.

But these are also confusing times for TV technology, with new acronyms and marketing terms raining down like confetti at the wedding of the managing director of a confetti company.

One of the key current confusions lies in the comparison between them and, as is so often the case, marketing is largely to blame - particularly from the QLED camp. So what exactly is the difference between OLED and QLED?

MORE: What is Ultra HD TV and 4K TV? Everything you need to know

OLED pros and cons

"The way the Sony A1 defines edges and reveals textures is beyond our already lofty expectations for this TV tech"

OLED (Organic Light-Emitting Diode) is a type of display tech that involves a carbon-based film being placed between two conductors that pass a current through and cause the film to emit a light.

What’s most important is that this light can be emitted on a pixel-by-pixel basis, so a bright white or coloured pixel can appear next to one that’s black or an entirely different colour, with neither impacting the other.

This is in direct contrast to a traditional LCD TV, which relies on a separate backlight to generate light that’s then passed through a layer of pixels.

Despite many attempts over the years, no TV with a backlight has ever managed to completely eradicate the issue of light bleeding from an intentionally bright pixel to those around it.

MORE: Sony KD-55A1 review

"[With the LG OLED55B7V] you never get the sense that what you’re watching is anything but precisely what was intended"

Other advantages of OLED are that the panels are lighter and thinner than a typical LCD/LED arrangement, viewing angles tend to be significantly wider, and response times can be supremely quick.

The major disadvantage is that OLEDs are very expensive to produce. Prices are beginning to get a little more realistic – thanks in no small part to LG (currently the only producer of OLED panels for TVs) selling panels to other manufacturers such as Sony and Panasonic, increasing both the amount being produced and competition in the shops – but OLED TVs still tend to be significantly more expensive than the alternatives.

For now, there isn’t an OLED TV available that’s smaller than 55in, either.

OLEDs also currently struggle to reach the same peak brightness levels of the best TVs that have a dedicated backlight.

MORE: What is OLED TV? The tech, the benefits, the best OLED TVs

More after the break

QLED pros and cons

"It’s the clarity and amount of detail within those bright and colourful moments [on the Samsung QE49Q7C] that really impresses"

The one major TV manufacturer not onboard the OLED train is Samsung, which is instead promoting a rival technology called QLED.

QLED stands for Quantum-dot Light-Emitting Diode which, in theory at least, has a great deal in common with OLED, most notably that each pixel can emit its own light, in this case thanks to quantum dots - tiny semiconductor particles only a few nanometres in size.

MORE: Samsung QE49Q7C review

"The biggest advantage an LCD TV with LED backlighting has over an OLED TV is brightness"

These quantum dots are (again, in theory) capable of giving off incredibly bright, vibrant and diverse colours – even more so than OLED.

The problem is that the quantum dots in current QLED TVs do not emit their own light. Instead they simply have the light from a backlight passed through them, in just the same way that an LCD layer does on non-QLED/LED backlit sets.

Quantum dots still improve colour vibrancy and control over LCD, but this isn’t the next-gen, game-changing technology that Samsung is suggesting with its QLED branding - it’s more a refinement of a technology the company was using in 2016.

MORE: Samsung QE55Q7F review

"Skin tones are well judged [on the Panasonic TX-55EZ95B], with natural colour and genuine subtlety."

But just because current QLEDs aren’t representative of endgame quantum dot tech doesn’t mean they should be written off. On the evidence of the models we’ve seen so far, QLEDs deliver significantly brighter, more vibrant pictures than their OLED rivals.

The current requirement that a quantum dot TV has a separate backlight does mean the compromises with LCD tech that we’ve been complaining about for years are still present. At the fairly minor end of the spectrum it means that panels simply can’t get as dramatically thin as an OLED - such as the LG OLED65W7 "wallpaper" TV.

But the major issue is that the overall brightness of the whole display still needs to be raised to light even a small, bright object at its centre, and that has a detrimental impact on the depth of black areas of the image.

Even with the Samsung QE55Q7F you occasionally notice the darkness of these areas (particularly the black bars at the top and bottom when watching a film) adjusting in accordance with the onscreen action – and that can be distracting.

OLED’s ability to light each pixel individually gives it a distinct advantage in that regard. While overall brightness levels are undeniably lower, contrast is still incredibly impressive.

If an image consists of very dark and very bright elements, OLEDs tend to combine the two more effectively, as shown by the Sony KD-55A1 and LG OLED55B7V.

The perfect TV technology would combine the brightness and vibrancy of current QLEDs with the black performance and uncompromised contrast of OLED, and current thinking is that the next-generation, genuinely light-emitting quantum dots could offer just that – to the extent that many manufacturers, including LG, are apparently working with that in mind.

Final verdict

There’s no telling how far away those next-gen QLEDs are, though, so for now a TV buyer is forced to choose which combination of strengths and compromises best suits their taste.

On the evidence of the sets we’ve seen so far, the more natural and authentic images offered by OLED just about trump the awesome punch of QLED.

But with Samsung’s current range generally costing significantly less than 2017’s OLEDs, there’s still a compelling case for its QLED screens.

See all our OLED TV reviews