OLED, or Organic Light Emitting Diodes, are the best advancement in display tech since LCD itself. Their inky blacks lead to image quality that outpaces traditional LCD, and unlike LCD-based displays they don't require a backlight, so they can be super-thin.

The advantages of OLED show up screens both tiny and huge.

Many of the the flagship smartphones currently use OLED displays. Samsung is the major producer of small screens OLED for phones, found not only in Samsung Galaxy phones but also in the Apple iPhone X, Google Pixel 2 and the OnePlus 5T.

CNET's picks for the best-performing TVs are OLED as well. LG Display is the only company currently producing big OLED screens TVs, found in LG TVs as well OLEDs by Sony and, outside the US, Panasonic and Philips.

LG also makes phone-size OLED screens, most notably in the the Pixel 2 XL, but that phone showed issues like burn-in and worse image quality that didn't affect Samsung-made OLED phone screens. On the TV side, LG's TV OLEDs are widely lauded, while Samsung hasn't sold an OLED TV since 2013.

Isn't OLED just OLED? Yes and no. Though the technology and methods are similar, the materials, how they're made, and so on can result in significant differences.

AMOLED and POLED: Most displays are both

Both Samsung and LG talk about AMOLED and POLED, both of which are ways to describe different parts of an OLED display.

"AM" stands for "active matrix," which describes how the individual OLED pixels are addressed. An OLED with a passive matrix would be fine for a fitness tracker, but anything you want to watch video on needs active matrix. Which is to say, as far as phones and TVs go, all OLEDs are active matrix. Samsung calling their OLEDs "AMOLED" is as redundant as if they called their LCDs "AMLCD" since they're also all active matrix.

The "P" in LG's marketing stands for "plastic," as opposed to glass. This refers to the base material of the OLED display (the "substrate"), not the front part you touch -- which is separate and often Gorilla Glass. Plastic is lighter and works better for phones, and allows the display to be more easily curved, which is why both Samsung and LG use it.

The main thing to know is that while not all POLEDs have to be AMOLEDs or vice versa, these days most OLED displays are both.

Or to put it another way, both Samsung and LG could call their current OLED phone displays OLED, POLED, AMOLED, or even PAMOLED, the last one to the delight of Pams everywhere, I'm sure.

RGB vs. WRGB subpixels: Different, but not necessarily better

Geoffrey Morrison/CNET

Every display is made up of tiny individual picture elements called pixels. Every pixel is made up of sub-pixels, usually one each of the primary colors of red, green and blue. Usually.

This is the big difference between the different types of OLED.

Samsung, with its phones and brief run at TV OLEDs, uses separate red, green and blue OLED materials to create the subpixels.

LG, for its phones and TVs, does not. Instead, it uses an RGB sandwich to create white light, and then uses color filters to create red, green, blue and white.

Or to put it another way, every subpixel in an LG OLED is "white," then a color filter on top determines what part of that white you see. For the first few years LG's OLEDs used a blue/yellow sandwich. According to LG, it now uses RGB.

This may seem unnecessarily complex. After all, if it's using red, green and blue OLEDs, why not just make red, green, and blue subpixels and ditch the inefficient color filters? Based on what it has said in the past, and what OLED experts I've spoken to have said, the sandwich allows it to minimize the effects of the blue OLED material aging faster than the other colors, which has been OLED's Achilles heel since its early days.

LG

Since every subpixel is the same, the whole panel ages at the same rate. The panel will get dimmer over time, but won't shift in color. Since LG claims its OLED TVs have similar lifespan as LCDs, it's clear there's something to this.

The manufacturing is also easier and therefore cheaper. In TV sizes this seems key, since LG has made large-panel OLED a reality, something no other manufacturer can so far claim. In phone sizes it doesn't seem to be as much of an issue, as Samsung has shown.

Pixels big and small

As you'd expect, the pixels on a phone are far smaller than those on a TV. The real reason isn't the manufacturing complexity, since they're both complex, but how they create light.

OLED is an emissive technology, as in it creates its own light. LCD, in comparison, is transmissive. The liquid crystals' main function is to block the light, to create the levels of gray to create an image. A separate backlight, typically composed of LEDs, creates the light.

LG

Because OLED pixels create their own light, the smaller they get, the less light they produce. A manufacturer could drive them with more power to make them brighter, but this creates a host of other issues, like battery life, heat, image retention and overall lifespan issues.

To get around this, phone OLEDs often use a "PenTile" or diamond arrangement. This means that instead of a simple square grid of red, green and blue subpixels, there are fewer red and blue subpixels compared to green. Which is to say, for a phone with a 2,436x1,125 resolution there are 2,436x1,125 (2,740,500) green subpixels, but only 1,370,250 each for red and blue. The red and blue subpixels are essentially "shared" with the adjacent green, which your eye is more sensitive to anyway. The below arrangement, used in the Samsung-built screen on the iPhone X, is one way to do this, but there are possible layouts.

Raymond Soneira/DisplayMate

TVs rarely use this method, Samsung's last plasma TV was one, since it can be visible with larger pixels. It works well with small and high-resolution displays since your eye can't discern it, and it's far more efficient to manufacture.

The future

OLED is the best of the present, and certainly the display of the near future -- which isn't to say it's perfect. Image retention, longevity, brightness, wider colors, efficiency and cost all can be improved. All of those things have been significantly improved over the past few decades, so there's little doubt they'll keep getting better.

What will be interesting is if Samsung, or another player, can get into the TV OLED space. LG, with its WRGB design, has seemingly figured out how to make OLED cost effectively. Hopefully we'll see someone else able to do the same. On the phone side there's already talk about some potential new players. Because really, it's also highly unlikely any manufacturer will return to LCD in their flagship phones.

Once you get used to the image quality of OLED, it's hard to go back.

Got a question for Geoff? First, check out all the other articles he's written on topics like why all HDMI cables are the same, TV resolutions explained, LED LCD vs. OLED and more. Still have a question? Tweet at him @TechWriterGeoff then check out his travel photography on Instagram. He also thinks you should check out his best-selling sci-fi novel and its sequel.

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