The Clever Tech Powering the New Apple Watch's Always-On Display

By David Nield on at

The Apple Watch Series 5 is the first of Apple’s smartwatches to come with an always-on display, so you no longer need to lift your wrist to see what the time is – one of the few features that Google’s Wear OS got first. This upgrade is made possible by a change in the screen tech on the Apple Watch, and we’re going to explain how it works.

First though, a brief history of the smart timepiece: the first Apple Watch appeared, you may remember, back in 2015, and it was... not fantastic. It came with an excellent OLED screen and impressed in terms of hardware design, but we found it laggy, fiddly to use, and slow – and that includes the time it took for the clock to appear when you raised your wrist to look at it.

After all, isn’t that the primary job of a watch? To tell the time? You can make the argument that a flick of the wrist isn’t too strenuous an exercise for seeing what hour of the day it is, but it’s often when your hands are busy doing something else – driving a car, riding the subway, washing the dishes – when you need to take a glance at the time.

Either that, or you need to check the time surreptitiously. When you’re chatting in a bar or sitting in a meeting, it’s not the best form to raise your wrist in front of you to wake up the Apple Watch display – people will inevitably think you’ve got somewhere better to be.

Of the upgrades we’ve seen to the Apple Watch since 2015, very few of them have involved the display, which has stayed largely unchanged until now. We’ve seen cellular connectivity added, improvements in speed and performance, and more and more watch faces, but the design hasn’t been modified much at all.

The brightness got bumped up with the “second-generation” OLED display in the Apple Watch Series 2, but the screen size and technology didn’t really shift until last year’s Apple Watch Series 4. That wearable bumped up the screen sizes to 40mm and 44mm (from 38mm and 42mm), as well as introducing the display tech that the always-on feature now takes advantage of: LTPO OLED.

That’s right: The killer feature of the Apple Watch 5 was actually built into the Apple Watch 4 too, but Apple didn’t take full advantage of it. Presumably, that’s because battery life wasn’t efficient enough, or there was some technical hurdle that meant the technology couldn’t be fully utilized until 2019, or Apple needed to refine the hardware further.

Whatever the reason, it’s here now thanks to something called LTPO – Low-Temperature Polycrystalline Oxide, or in Apple’s case, low-temperature polysilicon and oxide (a special, bespoke variation developed by Apple).

While Apple hasn’t gone into too much detail about how the screen on the Apple Watch 5 is put together, the fine folks at iFixit have provided an excellent explainer: Like every display, this one is made up of layers, including the pixels themselves and the circuitry controlling them (known as backplanes).

What Apple is actually doing here is mixing two different types of screen circuitry technology and getting the benefits from both. First, there’s low-temperature polycrystalline silicon (LTPS), the power-efficient tech found in many top-end OLED phone backplanes (including iPhones), which essentially controls whether a pixel is on or off.

Second, we have the more innovative Indium Gallium Zinc Oxide (IGZO) technology, which dictates the voltage supplied to each pixel, its brightness, and the particular mix of red, green and blue it’s using for its color. IGZO circuitry is already used in some Apple products, including iPads and MacBooks.

One of the end results is a variable refresh rate, as low as 1Hz (one refresh per second). Obviously that’s not enough to keep the second hand moving, but it is enough to tell you what the time is and how many steps you’ve done in a day. That lower refresh rate reduces power draw too, and combined with the dimmed brightness, the all-day battery life can be preserved.

It’s something that Apple has done before; the feature is implemented in a different way than the Apple Watch, but the iPad Pros feature ProMotion technology, able to change the refresh rate on the fly to improve responsiveness or to save energy.

The excellent power efficiency of LTPS, plus the way that IGZO handles lower display frequencies very well, is what helps make the Apple Watch 5 display special. Of course, it’s easier to do this sort of display circuitry manipulation on a smaller scale, so it might be some time before it appears in Apple’s phones and tablets.

LTPO isn’t working alone, according to Apple. “Several advanced technologies work together to deliver this new feature, including the industry’s only low-temperature polysilicon and oxide display (LTPO), ultra-low power display driver, efficient power management integrated circuit and new ambient light sensor,” the company explained

It’s a combination of these technologies that make the always-on display possible and enable it to go beyond what the LPTO-sporting Apple Watch 4 was able to do. As iFixit points out, space is also a consideration – anything that Apple does to improve the performance or functionality of its wearable has to fit inside the chassis dimensions that are being imposed.

As a note from last year by analysts IHS Markit explains, LTPO does have its challenges, including manufacturing complications and problems ramping up the resolution to be as high as it is with standard LTPS (IGZO-free) displays. Ultimately though, the investment could well be worth it in terms of energy efficiency – and Apple is likely to have at least one eye on folding displays further down the line.