Three-Minute Tech: AMOLED

[In our Three-Minute Tech series, we tell you everything you really need to know about a technology in three minutes or less.]

These days, you'll often see smartphones touting the superiority of their AMOLED (Active-Matrix Organic Light-Emitting Diode) or Super AMOLED displays. LG even touted the tech in a large TV. OLED (or AMOLED) display technology is great, and has a lot of benefits, but it isn't quite ready to replace all our LCDs just yet. Here's what you need to know about it.

How an LCD works

A Twisted Nematic LCD panel [source: PCWorld]

To begin with, I should describe how a traditional liquid-crystal display works. There are many types of LCDs, but all the ones in use today on smartphones, laptops, monitors, and TVs all work in basically the same way. A backlight (it can be flourescent lights or LEDs) shines through a film that polarizes the light. Then, it passes through the liquid crystal itself: this is the part that either blocks the light or lets it through, depending on whether or not it's charged with electricty.

The light that passes through the crystal then passes through a red, green, or blue plastic film to give the light color. LCDs make colors by mixing these three together in varying degrees. The light then passes through another polarizer, and finally to your eyes. This is a greatly simplified description, of course. There may be other filters and layers, including touch sensors.

What makes OLED different?

An OLED (Organic Light-Emitting Diode) display works in a fundamentally different fashion. Instead of shining a light through a series of filters and a liquid crystal that blocks some amount of light, OLEDs are basically special plastics that emit their own light when electricity is applied.

The basic structure of an OLED display [source: PCWorld]

This makes things a lot simpler. An OLED display has three kinds of polymers in it: one that emits red light when charged, one that emits green, and one that emits blue. A thin grid of electrodes applies a charge to the diodes and they light up. The more charge is applied, the brighter they shine.

This gives OLEDs a couple of big advantages over LCDs. First, there's no need for a backlight, because the polymers emit their own light. This helps allow OLED displays to be thinner than LCDs. Second, it makes black levels really, really black. On an LCD, black is usually achieved by trying to block out the backlight. On an OLED, a black pixel simply emits no light at all. Finally, OLEDs are extremely fast; they're able to change color many times faster than even the fastest LCD, which means no blurring or smearing when things move around quickly. And they look really good from all viewing angles.

If OLED is so great, why isn't everything OLED?

OLED displays have lots of benefits, but they're saddled with some equally big problems. The most obvious one is their cost. A good OLED display simply costs a lot more than a good LCD. Longevity can be an issue, too. The blue polymers start to loose their ability to produce light after thousands of hours; more quickly than the red or green polymers do. This leads to slight color shifting over very prolonged use. You won't notice on a smartphone you'll replace in a couple years, but you could see the effect after a decade of using an HDTV for hours a day. Longevity has improved in recent years, but it's still a little bit of a sore spot.

OLEDs were once considered very energy-efficient, but LCDs have caught up. OLED displays are far more effecient on screens where there's lots of black or dark colors, but can actually use more power than an effecient LCD on a bright screen with lots of white displayed.

What's AMOLED, then?

These days, you rarely see OLED advertised as a feature, you see "AMOLED". Although the extra stands for Active-Matrix, to be honest it's basically just marketing fluff. AM refers to the method by which the display controller chip tells the big 'ol matrix of pixels which ones should be lit up and which should not. Describing exactly how it works gets a little complicated, but what you really need to know is that nearly every digital display you use today—on your smartphone, laptop, or TV—is an active-matrix display.

Whether LCD or OLED, active-matrix is the norm. And that "Super AMOLED" stuff you see? That's a Samsung term for its AMOLED display that has the touch digitizer integrated into the display instead of laid on top of it.

For more on digital display technologies and how they work, check out Digital Displays Explained on PCWorld.

For comprehensive coverage of the Android ecosystem, visit Greenbot.com.

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