Category: Development

To date, Apple’s Retina displays have relied on LCD technologies. Since the iPhone 4, our mobile devices have used in-plane switching (IPS) technology to achieve high resolution with accurate color from a wide range of viewing angles. The IPS LCD panels are also present in many of the desktop monitors we use on our Macs.

Chances are good that’s about to change with an OLED display in the Apple Watch.

Unless you’ve done work on Android, you’re probably unaware how different AMOLED displays are from LCD. Let’s take a look at what lies ahead.

Physical Differences

An LCD display relies on a backlight that’s projected through three layers: one for each of the primary colors. Red, green and blue appear on screen because crystals in those layers can be aligned electrically to allow the backlight to pass through.

OLED has no backlight and has only one layer that produces light. That layer is an organic compound that emits light when subjected to an electric current. When you put them in a two dimensional matrix of transistors, you end up with an AMOLED display.

Based on these short descriptions, it’s easy to see why an OLED is thinner than its LCD counterpart: there are simply fewer layers of electronics. And it gets even better when you discover that the compounds and electronics can be fabricated on flexible plastic substrates.

LCDs have always been problematic in direct sunlight because the backlight must pass through filters which can also reflect ambient light. This has also been an issue for OLED displays where the light is emitted below a reflective metal cathode. The good news is that recent advances with the technology are producing brighter results than an LCD.

The biggest challenge for OLED is with the organic material where light is emitted. Basically, byproducts of the chemical reaction that produces light accumulate over time and reduce the efficiency of the output. Again, this is an area where manufacturers are focusing their efforts. In just a few years the lifespan of these devices have increased by several orders of magnitude, but is still limited to tens of thousands of hours. Don’t expect your Apple Watch to become a family heirloom.

How Not to Do It

OLED displays have gotten a bad rap on mobile devices primarily because of a thing called PenTile.

PenTile mimics how our eye works: 72% of the luminance we perceive is determined by the green wavelengths of the electromagnetic spectrum. The RGBG arrangement of sub-pixels lets a display get brighter without increasing the overall number of transistors needed. This, of course, keeps manufacturing costs down.

Unfortunately this physical layout of the light emitters also makes colors grainy and text hard to read. Color accuracy also suffers. PenTile is also a trademark of Samsung. I can’t see Apple using this approach in their Retina displays.

It’s much more likely that Apple’s industrial designers have been working hard to find a new and better way to use OLED technology without losing fidelity. I can’t wait for someone to look at the Apple Watch’s display under a microscope.

Black is Best

From Apple’s point-of-view, one of the most important things about OLED is how it consumes power. A transistor on the display only uses energy when it’s producing light. Compare this with an LCD backlight which must be lit in order to see any pixel.

Folks with OLED displays on their Android devices have figured out that a lot of black pixels makes their battery last longer. So too Apple.

It’s also important to remember that each pixel on the display has a limited lifetime. The less time the OLED spends producing light, the longer it lasts.

One of my first impressions of the Apple Watch user interface was that it used a lot of black. This makes the face of the device feel more expansive because you can’t see the edges. But more importantly, those black pixels are saving power and extending the life of the display. It’s rare that engineering and design goals can align so perfectly.

And from what we’ve seen so far of the watch, that black is really really black. We’ve become accustomed to blacks on LCD displays that aren’t really dark: that’s because the crystals that are blocking light let a small amount pass through. Total darkness lets the edgeless illusion work.

Flat Black

I’ve always felt that the flattening of Apple’s user interface that began in iOS 7 was as much a strategic move as an aesthetic one. Our first reaction was to realize that an unadorned interface makes it easier to focus on content.

But with this new display technology, it’s clear that interfaces with fewer pixels have another advantage. A richly detailed button from iOS 6 would need more of that precious juice strapped to our wrists. Never underestimate the long-term benefits of simplification.

The Future

Apple is a company that likes to leverage its technologies across a wide range of products. Look at how many of their devices are using IPS LCD displays now, then imagine a move to an OLED display pioneered by the Apple Watch.

When Jony Ive taps the home button on his iPhone and says, “The whole of the display comes on. That, to me, feels very, very old.” it’s a sign that individually addressable sources of light are the wave of the future.

Of course it will take time for this to happen, but you know it’s going to look awesome when they’re done. And along the way, we’ll learn to think about pixels differently.